1754 lines
64 KiB
Markdown
1754 lines
64 KiB
Markdown
Rhai - Embedded Scripting for Rust
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=================================
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[](http://travis-ci.org/jonathandturner/rhai)
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[](https://github.com/license/jonathandturner/rhai)
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[](https::/crates.io/crates/rhai/)
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[](https://docs.rs/rhai/)
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Rhai is an embedded scripting language and evaluation engine for Rust that gives a safe and easy way to add scripting to any application.
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Rhai's current features set:
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* `no-std` support
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* Easy integration with Rust functions and data types, supporting getter/setter methods
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* Easily call a script-defined function from Rust
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* Fairly efficient (1 million iterations in 0.75 sec on my 5 year old laptop)
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* Low compile-time overhead (~0.6 sec debug/~3 sec release for script runner app)
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* Easy-to-use language similar to JS+Rust
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* Support for overloaded functions
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* Compiled script is optimized for repeat evaluations
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* Very few additional dependencies (right now only [`num-traits`](https://crates.io/crates/num-traits/)
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to do checked arithmetic operations); for [`no_std`] builds, a number of additional dependencies are
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pulled in to provide for functionalities that used to be in `std`.
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**Note:** Currently, the version is 0.11.0, so the language and API's may change before they stabilize.
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Installation
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------------
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Install the Rhai crate by adding this line to `dependencies`:
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```toml
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[dependencies]
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rhai = "0.11.0"
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```
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Use the latest released crate version on [`crates.io`](https::/crates.io/crates/rhai/):
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```toml
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[dependencies]
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rhai = "*"
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```
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Crate versions are released on [`crates.io`](https::/crates.io/crates/rhai/) infrequently, so if you want to track the
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latest features, enhancements and bug fixes, pull directly from GitHub:
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```toml
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[dependencies]
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rhai = { git = "https://github.com/jonathandturner/rhai" }
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```
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Beware that in order to use pre-releases (e.g. alpha and beta), the exact version must be specified in the `Cargo.toml`.
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Optional features
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-----------------
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| Feature | Description |
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| ------------- | -------------------------------------------------------------------------------------------------------------------------------------------------------- |
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| `no_stdlib` | Exclude the standard library of utility functions in the build, and only include the minimum necessary functionalities. Standard types are not affected. |
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| `unchecked` | Exclude arithmetic checking (such as overflows and division by zero). Beware that a bad script may panic the entire system! |
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| `no_function` | Disable script-defined functions if not needed. |
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| `no_index` | Disable arrays and indexing features if not needed. |
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| `no_object` | Disable support for custom types and objects. |
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| `no_float` | Disable floating-point numbers and math if not needed. |
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| `no_optimize` | Disable the script optimizer. |
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| `only_i32` | Set the system integer type to `i32` and disable all other integer types. `INT` is set to `i32`. |
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| `only_i64` | Set the system integer type to `i64` and disable all other integer types. `INT` is set to `i64`. |
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| `no_std` | Build for `no-std`. Notice that additional dependencies will be pulled in to replace `std` features. |
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By default, Rhai includes all the standard functionalities in a small, tight package. Most features are here to opt-**out** of certain functionalities that are not needed.
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Excluding unneeded functionalities can result in smaller, faster builds as well as less bugs due to a more restricted language.
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[`unchecked`]: #optional-features
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[`no_stdlib`]: #optional-features
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[`no_index`]: #optional-features
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[`no_float`]: #optional-features
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[`no_function`]: #optional-features
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[`no_object`]: #optional-features
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[`no_optimize`]: #optional-features
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[`only_i32`]: #optional-features
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[`only_i64`]: #optional-features
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[`no_std`]: #optional-features
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Related
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-------
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Other cool projects to check out:
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* [ChaiScript](http://chaiscript.com/) - A strong inspiration for Rhai. An embedded scripting language for C++ that I helped created many moons ago, now being led by my cousin.
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* Check out the list of [scripting languages for Rust](https://github.com/rust-unofficial/awesome-rust#scripting) on [awesome-rust](https://github.com/rust-unofficial/awesome-rust)
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Examples
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--------
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A number of examples can be found in the `examples` folder:
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| Example | Description |
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| ------------------------------------------------------------------ | --------------------------------------------------------------------------- |
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| [`arrays_and_structs`](examples/arrays_and_structs.rs) | demonstrates registering a new type to Rhai and the usage of arrays on it |
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| [`custom_types_and_methods`](examples/custom_types_and_methods.rs) | shows how to register a type and methods for it |
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| [`hello`](examples/hello.rs) | simple example that evaluates an expression and prints the result |
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| [`no_std`](examples/no_std.rs) | example to test out `no-std` builds |
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| [`reuse_scope`](examples/reuse_scope.rs) | evaluates two pieces of code in separate runs, but using a common [`Scope`] |
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| [`rhai_runner`](examples/rhai_runner.rs) | runs each filename passed to it as a Rhai script |
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| [`simple_fn`](examples/simple_fn.rs) | shows how to register a Rust function to a Rhai [`Engine`] |
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| [`repl`](examples/repl.rs) | a simple REPL, interactively evaluate statements from stdin |
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Examples can be run with the following command:
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```bash
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cargo run --example name
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```
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The `repl` example is a particularly good one as it allows you to interactively try out Rhai's
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language features in a standard REPL (**R**ead-**E**val-**P**rint **L**oop).
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Example Scripts
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---------------
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There are also a number of examples scripts that showcase Rhai's features, all in the `scripts` folder:
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| Language feature scripts | Description |
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| ---------------------------------------------------- | ------------------------------------------------------------- |
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| [`array.rhai`](scripts/array.rhai) | arrays in Rhai |
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| [`assignment.rhai`](scripts/assignment.rhai) | variable declarations |
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| [`comments.rhai`](scripts/comments.rhai) | just comments |
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| [`for1.rhai`](scripts/for1.rhai) | for loops |
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| [`function_decl1.rhai`](scripts/function_decl1.rhai) | a function without parameters |
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| [`function_decl2.rhai`](scripts/function_decl2.rhai) | a function with two parameters |
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| [`function_decl3.rhai`](scripts/function_decl3.rhai) | a function with many parameters |
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| [`if1.rhai`](scripts/if1.rhai) | if example |
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| [`loop.rhai`](scripts/loop.rhai) | endless loop in Rhai, this example emulates a do..while cycle |
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| [`op1.rhai`](scripts/op1.rhai) | just a simple addition |
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| [`op2.rhai`](scripts/op2.rhai) | simple addition and multiplication |
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| [`op3.rhai`](scripts/op3.rhai) | change evaluation order with parenthesis |
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| [`string.rhai`](scripts/string.rhai) | string operations |
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| [`while.rhai`](scripts/while.rhai) | while loop |
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| Example scripts | Description |
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| -------------------------------------------- | ---------------------------------------------------------------------------------- |
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| [`speed_test.rhai`](scripts/speed_test.rhai) | a simple program to measure the speed of Rhai's interpreter (1 million iterations) |
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| [`primes.rhai`](scripts/primes.rhai) | use Sieve of Eratosthenes to find all primes smaller than a limit |
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To run the scripts, either make a tiny program or use of the `rhai_runner` example:
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```bash
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cargo run --example rhai_runner scripts/any_script.rhai
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```
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Hello world
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-----------
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[`Engine`]: #hello-world
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To get going with Rhai, create an instance of the scripting engine and then call `eval`:
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```rust
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use rhai::{Engine, EvalAltResult};
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fn main() -> Result<(), EvalAltResult>
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{
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let mut engine = Engine::new();
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let result = engine.eval::<i64>("40 + 2")?;
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println!("Answer: {}", result); // prints 42
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Ok(())
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}
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```
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The type parameter is used to specify the type of the return value, which _must_ match the actual type or an error is returned.
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Rhai is very strict here. There are two ways to specify the return type - _turbofish_ notation, or type inference.
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```rust
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let result = engine.eval::<i64>("40 + 2")?; // return type is i64, specified using 'turbofish' notation
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let result: i64 = engine.eval("40 + 2")?; // return type is inferred to be i64
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let result = engine.eval::<String>("40 + 2")?; // returns an error because the actual return type is i64, not String
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```
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Evaluate a script file directly:
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```rust
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let result = engine.eval_file::<i64>("hello_world.rhai".into())?; // 'eval_file' takes a 'PathBuf'
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```
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To repeatedly evaluate a script, _compile_ it first into an AST (abstract syntax tree) form:
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```rust
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// Compile to an AST and store it for later evaluations
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let ast = engine.compile("40 + 2")?;
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for _ in 0..42 {
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let result: i64 = engine.eval_ast(&ast)?;
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println!("Answer #{}: {}", i, result); // prints 42
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}
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```
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Compiling a script file is also supported:
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```rust
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let ast = engine.compile_file("hello_world.rhai".into())?;
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```
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Rhai also allows working _backwards_ from the other direction - i.e. calling a Rhai-scripted function from Rust - via `call_fn`:
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```rust
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// Define a function in a script and load it into the Engine.
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// Pass true to 'retain_functions' otherwise these functions will be cleared at the end of consume()
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engine.consume(true,
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r"
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// a function with two parameters: String and i64
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fn hello(x, y) {
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x.len() + y
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}
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// functions can be overloaded: this one takes only one parameter
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fn hello(x) {
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x * 2
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}
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")?;
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// Evaluate the function in the AST, passing arguments into the script as a tuple
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// if there are more than one. Beware, arguments must be of the correct types because
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// Rhai does not have built-in type conversions. If arguments of the wrong types are passed,
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// the Engine will not find the function.
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let result: i64 = engine.call_fn("hello", &ast, ( String::from("abc"), 123_i64 ) )?;
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// ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ put arguments in a tuple
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let result: i64 = engine.call_fn("hello", 123_i64)?
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// ^^^^^^^ calls 'hello' with one parameter (no need for tuple)
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```
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Evaluate expressions only
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-------------------------
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Sometimes a use case does not require a full-blown scripting _language_, but only needs to evaluate _expressions_.
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In these cases, use the `compile_expression` and `eval_expression` methods or their `_with_scope` variants.
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```rust
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let result = engine.eval_expression::<i64>("2 + (10 + 10) * 2")?;
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```
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When evaluation _expressions_, no control-flow statement (e.g. `if`, `while`, `for`) is not supported and will be
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parse errors when encountered - not even variable assignments.
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```rust
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// The following are all syntax errors because the script is not an expression.
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engine.eval_expression::<()>("x = 42")?;
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let ast = engine.compile_expression("let x = 42")?;
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let result = engine.eval_expression_with_scope::<i64>(&mut scope, "if x { 42 } else { 123 }")?;
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```
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Values and types
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----------------
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[`type_of()`]: #values-and-types
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[`to_string()`]: #values-and-types
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The following primitive types are supported natively:
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| Category | Equivalent Rust types | `type_of()` | `to_string()` |
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| ----------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | --------------------- | --------------------- |
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| **Integer number** | `u8`, `i8`, `u16`, `i16`, <br/>`u32`, `i32` (default for [`only_i32`]),<br/>`u64`, `i64` _(default)_ | `"i32"`, `"u64"` etc. | `"42"`, `"123"` etc. |
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| **Floating-point number** (disabled with [`no_float`]) | `f32`, `f64` _(default)_ | `"f32"` or `"f64"` | `"123.4567"` etc. |
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| **Boolean value** | `bool` | `"bool"` | `"true"` or `"false"` |
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| **Unicode character** | `char` | `"char"` | `"A"`, `"x"` etc. |
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| **Unicode string** | `String` (_not_ `&str`) | `"string"` | `"hello"` etc. |
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| **Array** (disabled with [`no_index`]) | `rhai::Array` | `"array"` | `"[ ? ? ? ]"` |
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| **Object map** (disabled with [`no_object`]) | `rhai::Map` | `"map"` | `#{ "a": 1, "b": 2 }` |
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| **Dynamic value** (i.e. can be anything) | `rhai::Dynamic` | _the actual type_ | _actual value_ |
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| **System integer** (current configuration) | `rhai::INT` (`i32` or `i64`) | `"i32"` or `"i64"` | `"42"`, `"123"` etc. |
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| **System floating-point** (current configuration, disabled with [`no_float`]) | `rhai::FLOAT` (`f32` or `f64`) | `"f32"` or `"f64"` | `"123.456"` etc. |
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| **Nothing/void/nil/null** (or whatever you want to call it) | `()` | `"()"` | `""` _(empty string)_ |
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[`Dynamic`]: #values-and-types
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[`()`]: #values-and-types
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All types are treated strictly separate by Rhai, meaning that `i32` and `i64` and `u32` are completely different - they even cannot be added together. This is very similar to Rust.
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The default integer type is `i64`. If other integer types are not needed, it is possible to exclude them and make a smaller build with the [`only_i64`] feature.
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If only 32-bit integers are needed, enabling the [`only_i32`] feature will remove support for all integer types other than `i32`, including `i64`.
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This is useful on some 32-bit systems where using 64-bit integers incurs a performance penalty.
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If no floating-point is needed or supported, use the [`no_float`] feature to remove it.
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The `to_string` function converts a standard type into a string for display purposes.
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The `type_of` function detects the actual type of a value. This is useful because all variables are `Dynamic`.
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```rust
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// Use 'type_of()' to get the actual types of values
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type_of('c') == "char";
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type_of(42) == "i64";
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let x = 123;
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x.type_of(); // <- error: 'type_of' cannot use method-call style
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type_of(x) == "i64";
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x = 99.999;
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type_of(x) == "f64";
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x = "hello";
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if type_of(x) == "string" {
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do_something_with_string(x);
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}
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```
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Value conversions
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-----------------
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[`to_int`]: #value-conversions
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[`to_float`]: #value-conversions
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The `to_float` function converts a supported number to `FLOAT` (`f32` or `f64`),
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and the `to_int` function converts a supported number to `INT` (`i32` or `i64`).
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That's about it. For other conversions, register custom conversion functions.
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```rust
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let x = 42;
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let y = x * 100.0; // <- error: cannot multiply i64 with f64
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let y = x.to_float() * 100.0; // works
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let z = y.to_int() + x; // works
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let c = 'X'; // character
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print("c is '" + c + "' and its code is " + c.to_int()); // prints "c is 'X' and its code is 88"
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```
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Working with functions
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----------------------
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Rhai's scripting engine is very lightweight. It gets most of its abilities from functions.
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To call these functions, they need to be registered with the [`Engine`].
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```rust
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use rhai::{Engine, EvalAltResult};
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use rhai::RegisterFn; // use `RegisterFn` trait for `register_fn`
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use rhai::{Dynamic, RegisterDynamicFn}; // use `RegisterDynamicFn` trait for `register_dynamic_fn`
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// Normal function
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fn add(x: i64, y: i64) -> i64 {
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x + y
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}
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// Function that returns a Dynamic value
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fn get_an_any() -> Dynamic {
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Box::new(42_i64)
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}
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fn main() -> Result<(), EvalAltResult>
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{
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let mut engine = Engine::new();
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engine.register_fn("add", add);
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let result = engine.eval::<i64>("add(40, 2)")?;
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println!("Answer: {}", result); // prints 42
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// Functions that return Dynamic values must use register_dynamic_fn()
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engine.register_dynamic_fn("get_an_any", get_an_any);
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let result = engine.eval::<i64>("get_an_any()")?;
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println!("Answer: {}", result); // prints 42
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Ok(())
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}
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```
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To return a [`Dynamic`] value from a Rust function, simply `Box` it and return it.
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```rust
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fn decide(yes_no: bool) -> Dynamic {
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if yes_no {
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Box::new(42_i64)
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} else {
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Box::new("hello world!".to_string()) // remember &str is not supported
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}
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}
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```
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Generic functions
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-----------------
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Generic functions can be used in Rhai, but separate instances for each concrete type must be registered separately:
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```rust
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use std::fmt::Display;
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use rhai::{Engine, RegisterFn};
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fn show_it<T: Display>(x: &mut T) -> () {
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println!("put up a good show: {}!", x)
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}
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fn main()
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{
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let mut engine = Engine::new();
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engine.register_fn("print", show_it as fn(x: &mut i64)->());
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engine.register_fn("print", show_it as fn(x: &mut bool)->());
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engine.register_fn("print", show_it as fn(x: &mut String)->());
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}
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```
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This example shows how to register multiple functions (or, in this case, multiple instances of the same function) to the same name in script.
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This enables function overloading based on the number and types of parameters.
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Fallible functions
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------------------
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If a function is _fallible_ (i.e. it returns a `Result<_, Error>`), it can be registered with `register_result_fn` (using the `RegisterResultFn` trait).
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The function must return `Result<_, EvalAltResult>`. `EvalAltResult` implements `From<&str>` and `From<String>` etc. and the error text gets converted into `EvalAltResult::ErrorRuntime`.
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```rust
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use rhai::{Engine, EvalAltResult, Position};
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use rhai::RegisterResultFn; // use `RegisterResultFn` trait for `register_result_fn`
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// Function that may fail
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fn safe_divide(x: i64, y: i64) -> Result<i64, EvalAltResult> {
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if y == 0 {
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// Return an error if y is zero
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Err("Division by zero detected!".into()) // short-cut to create EvalAltResult
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} else {
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Ok(x / y)
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}
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}
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fn main()
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{
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let mut engine = Engine::new();
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// Fallible functions that return Result values must use register_result_fn()
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engine.register_result_fn("divide", safe_divide);
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if let Err(error) = engine.eval::<i64>("divide(40, 0)") {
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println!("Error: {:?}", error); // prints ErrorRuntime("Division by zero detected!", (1, 1)")
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}
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}
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```
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Overriding built-in functions
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----------------------------
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|
|
|
Any similarly-named function defined in a script overrides any built-in function.
|
|
|
|
```rust
|
|
// Override the built-in function 'to_int'
|
|
fn to_int(num) {
|
|
print("Ha! Gotcha! " + num);
|
|
}
|
|
|
|
print(to_int(123)); // what happens?
|
|
```
|
|
|
|
Custom types and methods
|
|
-----------------------
|
|
|
|
Here's an more complete example of working with Rust. First the example, then we'll break it into parts:
|
|
|
|
```rust
|
|
use rhai::{Engine, EvalAltResult};
|
|
use rhai::RegisterFn;
|
|
|
|
#[derive(Clone)]
|
|
struct TestStruct {
|
|
field: i64
|
|
}
|
|
|
|
impl TestStruct {
|
|
fn update(&mut self) {
|
|
self.field += 41;
|
|
}
|
|
|
|
fn new() -> Self {
|
|
TestStruct { field: 1 }
|
|
}
|
|
}
|
|
|
|
fn main() -> Result<(), EvalAltResult>
|
|
{
|
|
let mut engine = Engine::new();
|
|
|
|
engine.register_type::<TestStruct>();
|
|
|
|
engine.register_fn("update", TestStruct::update);
|
|
engine.register_fn("new_ts", TestStruct::new);
|
|
|
|
let result = engine.eval::<TestStruct>("let x = new_ts(); x.update(); x")?;
|
|
|
|
println!("result: {}", result.field); // prints 42
|
|
|
|
Ok(())
|
|
}
|
|
```
|
|
|
|
All custom types must implement `Clone`. This allows the [`Engine`] to pass by value.
|
|
You can turn off support for custom types via the [`no_object`] feature.
|
|
|
|
```rust
|
|
#[derive(Clone)]
|
|
struct TestStruct {
|
|
field: i64
|
|
}
|
|
```
|
|
|
|
Next, we create a few methods that we'll later use in our scripts. Notice that we register our custom type with the [`Engine`].
|
|
|
|
```rust
|
|
impl TestStruct {
|
|
fn update(&mut self) {
|
|
self.field += 41;
|
|
}
|
|
|
|
fn new() -> Self {
|
|
TestStruct { field: 1 }
|
|
}
|
|
}
|
|
|
|
let mut engine = Engine::new();
|
|
|
|
engine.register_type::<TestStruct>();
|
|
```
|
|
|
|
To use methods and functions with the [`Engine`], we need to register them. There are some convenience functions to help with this.
|
|
Below I register update and new with the [`Engine`].
|
|
|
|
*Note: [`Engine`] follows the convention that methods use a `&mut` first parameter so that invoking methods can update the value in memory.*
|
|
|
|
```rust
|
|
engine.register_fn("update", TestStruct::update); // registers 'update(&mut ts)'
|
|
engine.register_fn("new_ts", TestStruct::new); // registers 'new'
|
|
```
|
|
|
|
Finally, we call our script. The script can see the function and method we registered earlier.
|
|
We need to get the result back out from script land just as before, this time casting to our custom struct type.
|
|
|
|
```rust
|
|
let result = engine.eval::<TestStruct>("let x = new_ts(); x.update(); x")?;
|
|
|
|
println!("result: {}", result.field); // prints 42
|
|
```
|
|
|
|
In fact, any function with a first argument (either by copy or via a `&mut` reference) can be used as a method-call on that type because internally they are the same thing:
|
|
methods on a type is implemented as a functions taking an first argument.
|
|
|
|
```rust
|
|
fn foo(ts: &mut TestStruct) -> i64 {
|
|
ts.field
|
|
}
|
|
|
|
engine.register_fn("foo", foo);
|
|
|
|
let result = engine.eval::<i64>("let x = new_ts(); x.foo()")?;
|
|
|
|
println!("result: {}", result); // prints 1
|
|
```
|
|
|
|
If the [`no_object`] feature is turned on, however, the _method_ style of function calls (i.e. calling a function as an object-method) is no longer supported.
|
|
|
|
```rust
|
|
// Below is a syntax error under 'no_object' because 'len' cannot be called in method style.
|
|
let result = engine.eval::<i64>("let x = [1, 2, 3]; x.len()")?;
|
|
```
|
|
|
|
[`type_of()`] works fine with custom types and returns the name of the type.
|
|
If `register_type_with_name` is used to register the custom type
|
|
with a special "pretty-print" name, [`type_of()`] will return that name instead.
|
|
|
|
```rust
|
|
engine.register_type::<TestStruct>();
|
|
engine.register_fn("new_ts", TestStruct::new);
|
|
let x = new_ts();
|
|
print(type_of(x)); // prints "path::to::module::TestStruct"
|
|
|
|
engine.register_type_with_name::<TestStruct>("Hello");
|
|
engine.register_fn("new_ts", TestStruct::new);
|
|
let x = new_ts();
|
|
print(type_of(x)); // prints "Hello"
|
|
```
|
|
|
|
Getters and setters
|
|
-------------------
|
|
|
|
Similarly, custom types can expose members by registering a `get` and/or `set` function.
|
|
|
|
```rust
|
|
#[derive(Clone)]
|
|
struct TestStruct {
|
|
field: i64
|
|
}
|
|
|
|
impl TestStruct {
|
|
fn get_field(&mut self) -> i64 {
|
|
self.field
|
|
}
|
|
|
|
fn set_field(&mut self, new_val: i64) {
|
|
self.field = new_val;
|
|
}
|
|
|
|
fn new() -> Self {
|
|
TestStruct { field: 1 }
|
|
}
|
|
}
|
|
|
|
let mut engine = Engine::new();
|
|
|
|
engine.register_type::<TestStruct>();
|
|
|
|
engine.register_get_set("xyz", TestStruct::get_field, TestStruct::set_field);
|
|
engine.register_fn("new_ts", TestStruct::new);
|
|
|
|
let result = engine.eval::<i64>("let a = new_ts(); a.xyz = 42; a.xyz")?;
|
|
|
|
println!("Answer: {}", result); // prints 42
|
|
```
|
|
|
|
Needless to say, `register_type`, `register_type_with_name`, `register_get`, `register_set` and `register_get_set`
|
|
are not available when the [`no_object`] feature is turned on.
|
|
|
|
Initializing and maintaining state
|
|
---------------------------------
|
|
|
|
[`Scope`]: #initializing-and-maintaining-state
|
|
|
|
By default, Rhai treats each [`Engine`] invocation as a fresh one, persisting only the functions that have been defined but no global state.
|
|
This gives each evaluation a clean starting slate. In order to continue using the same global state from one invocation to the next,
|
|
such a state must be manually created and passed in.
|
|
|
|
In this example, a global state object (a `Scope`) is created with a few initialized variables, then the same state is threaded through multiple invocations:
|
|
|
|
```rust
|
|
use rhai::{Engine, Scope, EvalAltResult};
|
|
|
|
fn main() -> Result<(), EvalAltResult>
|
|
{
|
|
let mut engine = Engine::new();
|
|
|
|
// First create the state
|
|
let mut scope = Scope::new();
|
|
|
|
// Then push some initialized variables into the state
|
|
// NOTE: Remember the system number types in Rhai are i64 (i32 if 'only_i32') ond f64.
|
|
// Better stick to them or it gets hard working with the script.
|
|
scope.push("y", 42_i64);
|
|
scope.push("z", 999_i64);
|
|
scope.push("s", "hello, world!".to_string()); // remember to use 'String', not '&str'
|
|
|
|
// First invocation
|
|
engine.eval_with_scope::<()>(&mut scope, r"
|
|
let x = 4 + 5 - y + z + s.len();
|
|
y = 1;
|
|
")?;
|
|
|
|
// Second invocation using the same state
|
|
let result = engine.eval_with_scope::<i64>(&mut scope, "x")?;
|
|
|
|
println!("result: {}", result); // prints 979
|
|
|
|
// Variable y is changed in the script
|
|
assert_eq!(scope.get_value::<i64>("y").expect("variable x should exist"), 1);
|
|
|
|
Ok(())
|
|
}
|
|
```
|
|
|
|
Engine configuration options
|
|
---------------------------
|
|
|
|
| Method | Description |
|
|
| ------------------------ | ---------------------------------------------------------------------------------------- |
|
|
| `set_optimization_level` | Set the amount of script _optimizations_ performed. See [`script optimization`]. |
|
|
| `set_max_call_levels` | Set the maximum number of function call levels (default 50) to avoid infinite recursion. |
|
|
|
|
[`script optimization`]: #script-optimization
|
|
|
|
-------
|
|
|
|
Rhai Language Guide
|
|
===================
|
|
|
|
Comments
|
|
--------
|
|
|
|
Comments are C-style, including '`/*` ... `*/`' pairs and '`//`' for comments to the end of the line.
|
|
|
|
```rust
|
|
let /* intruder comment */ name = "Bob";
|
|
|
|
// This is a very important comment
|
|
|
|
/* This comment spans
|
|
multiple lines, so it
|
|
only makes sense that
|
|
it is even more important */
|
|
|
|
/* Fear not, Rhai satisfies all nesting needs with nested comments:
|
|
/*/*/*/*/**/*/*/*/*/
|
|
*/
|
|
```
|
|
|
|
Statements
|
|
----------
|
|
|
|
Statements are terminated by semicolons '`;`' - they are mandatory, except for the _last_ statement where it can be omitted.
|
|
|
|
A statement can be used anywhere where an expression is expected. The _last_ statement of a statement block
|
|
(enclosed by '`{`' .. '`}`' pairs) is always the return value of the statement. If a statement has no return value
|
|
(e.g. variable definitions, assignments) then the value will be [`()`].
|
|
|
|
```rust
|
|
let a = 42; // normal assignment statement
|
|
let a = foo(42); // normal function call statement
|
|
foo < 42; // normal expression as statement
|
|
|
|
let a = { 40 + 2 }; // 'a' is set to the value of the statement block, which is the value of the last statement
|
|
// ^ notice that the last statement does not require a terminating semicolon (although it also works with it)
|
|
// ^ notice that a semicolon is required here to terminate the assignment statement; it is syntax error without it
|
|
|
|
4 * 10 + 2 // this is also a statement, which is an expression, with no ending semicolon because
|
|
// it is the last statement of the whole block
|
|
```
|
|
|
|
Variables
|
|
---------
|
|
|
|
[variables]: #variables
|
|
|
|
Variables in Rhai follow normal C naming rules (i.e. must contain only ASCII letters, digits and underscores '`_`').
|
|
|
|
Variable names must start with an ASCII letter or an underscore '`_`', must contain at least one ASCII letter, and must start with an ASCII letter before a digit.
|
|
Therefore, names like '`_`', '`_42`', '`3a`' etc. are not legal variable names, but '`_c3po`' and '`r2d2`' are.
|
|
Variable names are also case _sensitive_.
|
|
|
|
Variables are defined using the `let` keyword. A variable defined within a statement block is _local_ to that block.
|
|
|
|
```rust
|
|
let x = 3; // ok
|
|
let _x = 42; // ok
|
|
let x_ = 42; // also ok
|
|
let _x_ = 42; // still ok
|
|
|
|
let _ = 123; // <- syntax error: illegal variable name
|
|
let _9 = 9; // <- syntax error: illegal variable name
|
|
|
|
let x = 42; // variable is 'x', lower case
|
|
let X = 123; // variable is 'X', upper case
|
|
x == 42;
|
|
X == 123;
|
|
|
|
{
|
|
let x = 999; // local variable 'x' shadows the 'x' in parent block
|
|
x == 999; // access to local 'x'
|
|
}
|
|
x == 42; // the parent block's 'x' is not changed
|
|
```
|
|
|
|
Constants
|
|
---------
|
|
|
|
Constants can be defined using the `const` keyword and are immutable. Constants follow the same naming rules as [variables].
|
|
|
|
```rust
|
|
const x = 42;
|
|
print(x * 2); // prints 84
|
|
x = 123; // <- syntax error: cannot assign to constant
|
|
```
|
|
|
|
Constants must be assigned a _value_, not an expression.
|
|
|
|
```rust
|
|
const x = 40 + 2; // <- syntax error: cannot assign expression to constant
|
|
```
|
|
|
|
Numbers
|
|
-------
|
|
|
|
Integer numbers follow C-style format with support for decimal, binary ('`0b`'), octal ('`0o`') and hex ('`0x`') notations.
|
|
|
|
The default system integer type (also aliased to `INT`) is `i64`. It can be turned into `i32` via the [`only_i32`] feature.
|
|
|
|
Floating-point numbers are also supported if not disabled with [`no_float`]. The default system floating-point type is `i64` (also aliased to `FLOAT`).
|
|
|
|
'`_`' separators can be added freely and are ignored within a number.
|
|
|
|
| Format | Type |
|
|
| ---------------- | ---------------- |
|
|
| `123_345`, `-42` | `i64` in decimal |
|
|
| `0o07_76` | `i64` in octal |
|
|
| `0xabcd_ef` | `i64` in hex |
|
|
| `0b0101_1001` | `i64` in binary |
|
|
| `123_456.789` | `f64` |
|
|
|
|
Numeric operators
|
|
-----------------
|
|
|
|
Numeric operators generally follow C styles.
|
|
|
|
| Operator | Description | Integers only |
|
|
| -------- | ---------------------------------------------------- | :-----------: |
|
|
| `+` | Plus | |
|
|
| `-` | Minus | |
|
|
| `*` | Multiply | |
|
|
| `/` | Divide (integer division if acting on integer types) | |
|
|
| `%` | Modulo (remainder) | |
|
|
| `~` | Power | |
|
|
| `&` | Binary _And_ bit-mask | Yes |
|
|
| `\|` | Binary _Or_ bit-mask | Yes |
|
|
| `^` | Binary _Xor_ bit-mask | Yes |
|
|
| `<<` | Left bit-shift | Yes |
|
|
| `>>` | Right bit-shift | Yes |
|
|
|
|
```rust
|
|
let x = (1 + 2) * (6 - 4) / 2; // arithmetic, with parentheses
|
|
let reminder = 42 % 10; // modulo
|
|
let power = 42 ~ 2; // power (i64 and f64 only)
|
|
let left_shifted = 42 << 3; // left shift
|
|
let right_shifted = 42 >> 3; // right shift
|
|
let bit_op = 42 | 99; // bit masking
|
|
```
|
|
|
|
Unary operators
|
|
---------------
|
|
|
|
| Operator | Description |
|
|
| -------- | ----------- |
|
|
| `+` | Plus |
|
|
| `-` | Negative |
|
|
|
|
```rust
|
|
let number = -5;
|
|
number = -5 - +5;
|
|
```
|
|
|
|
Numeric functions
|
|
-----------------
|
|
|
|
The following standard functions (defined in the standard library but excluded if [`no_stdlib`]) operate on `i8`, `i16`, `i32`, `i64`, `f32` and `f64` only:
|
|
|
|
| Function | Description |
|
|
| ------------ | --------------------------------- |
|
|
| `abs` | absolute value |
|
|
| [`to_float`] | converts an integer type to `f64` |
|
|
|
|
Floating-point functions
|
|
------------------------
|
|
|
|
The following standard functions (defined in the standard library but excluded if [`no_stdlib`]) operate on `f64` only:
|
|
|
|
| Category | Functions |
|
|
| ---------------- | ------------------------------------------------------------ |
|
|
| Trigonometry | `sin`, `cos`, `tan`, `sinh`, `cosh`, `tanh` in degrees |
|
|
| Arc-trigonometry | `asin`, `acos`, `atan`, `asinh`, `acosh`, `atanh` in degrees |
|
|
| Square root | `sqrt` |
|
|
| Exponential | `exp` (base _e_) |
|
|
| Logarithmic | `ln` (base _e_), `log10` (base 10), `log` (any base) |
|
|
| Rounding | `floor`, `ceiling`, `round`, `int`, `fraction` |
|
|
| Conversion | [`to_int`] |
|
|
| Testing | `is_nan`, `is_finite`, `is_infinite` |
|
|
|
|
Strings and Chars
|
|
-----------------
|
|
|
|
String and char literals follow C-style formatting, with support for Unicode ('`\u`_xxxx_' or '`\U`_xxxxxxxx_') and hex ('`\x`_xx_') escape sequences.
|
|
|
|
Hex sequences map to ASCII characters, while '`\u`' maps to 16-bit common Unicode code points and '`\U`' maps the full, 32-bit extended Unicode code points.
|
|
|
|
Internally Rhai strings are stored as UTF-8 just like Rust (they _are_ Rust `String`s!), but there are major differences.
|
|
In Rhai a string is the same as an array of Unicode characters and can be directly indexed (unlike Rust).
|
|
This is similar to most other languages where strings are internally represented not as UTF-8 but as arrays of multi-byte Unicode characters.
|
|
Individual characters within a Rhai string can also be replaced just as if the string is an array of Unicode characters.
|
|
In Rhai, there is also no separate concepts of `String` and `&str` as in Rust.
|
|
|
|
Strings can be built up from other strings and types via the `+` operator (provided by the standard library but excluded if [`no_stdlib`]).
|
|
This is particularly useful when printing output.
|
|
|
|
[`type_of()`] a string returns `"string"`.
|
|
|
|
```rust
|
|
let name = "Bob";
|
|
let middle_initial = 'C';
|
|
let last = "Davis";
|
|
|
|
let full_name = name + " " + middle_initial + ". " + last;
|
|
full_name == "Bob C. Davis";
|
|
|
|
// String building with different types
|
|
let age = 42;
|
|
let record = full_name + ": age " + age;
|
|
record == "Bob C. Davis: age 42";
|
|
|
|
// Unlike Rust, Rhai strings can be indexed to get a character
|
|
// (disabled with 'no_index')
|
|
let c = record[4];
|
|
c == 'C';
|
|
|
|
ts.s = record; // custom type properties can take strings
|
|
|
|
let c = ts.s[4];
|
|
c == 'C';
|
|
|
|
let c = "foo"[0]; // indexing also works on string literals...
|
|
c == 'f';
|
|
|
|
let c = ("foo" + "bar")[5]; // ... and expressions returning strings
|
|
c == 'r';
|
|
|
|
// Escape sequences in strings
|
|
record += " \u2764\n"; // escape sequence of '❤' in Unicode
|
|
record == "Bob C. Davis: age 42 ❤\n"; // '\n' = new-line
|
|
|
|
// Unlike Rust, Rhai strings can be directly modified character-by-character
|
|
// (disabled with 'no_index')
|
|
record[4] = '\x58'; // 0x58 = 'X'
|
|
record == "Bob X. Davis: age 42 ❤\n";
|
|
```
|
|
|
|
The following standard functions (defined in the standard library but excluded if [`no_stdlib`]) operate on strings:
|
|
|
|
| Function | Description |
|
|
| ---------- | ------------------------------------------------------------------------ |
|
|
| `len` | returns the number of characters (not number of bytes) in the string |
|
|
| `pad` | pads the string with an character until a specified number of characters |
|
|
| `append` | Adds a character or a string to the end of another string |
|
|
| `clear` | empties the string |
|
|
| `truncate` | cuts off the string at exactly a specified number of characters |
|
|
| `contains` | checks if a certain character or sub-string occurs in the string |
|
|
| `replace` | replaces a substring with another |
|
|
| `trim` | trims the string |
|
|
|
|
Examples:
|
|
|
|
```rust
|
|
let full_name == " Bob C. Davis ";
|
|
full_name.len() == 14;
|
|
|
|
full_name.trim();
|
|
full_name.len() == 12;
|
|
full_name == "Bob C. Davis";
|
|
|
|
full_name.pad(15, '$');
|
|
full_name.len() == 15;
|
|
full_name == "Bob C. Davis$$$";
|
|
|
|
full_name.truncate(6);
|
|
full_name.len() == 6;
|
|
full_name == "Bob C.";
|
|
|
|
full_name.replace("Bob", "John");
|
|
full_name.len() == 7;
|
|
full_name = "John C.";
|
|
|
|
full_name.contains('C') == true;
|
|
full_name.contains("John") == true;
|
|
|
|
full_name.clear();
|
|
full_name.len() == 0;
|
|
```
|
|
|
|
Arrays
|
|
------
|
|
|
|
Arrays are first-class citizens in Rhai. Like C, arrays are accessed with zero-based, non-negative integer indices.
|
|
Array literals are built within square brackets '`[`' ... '`]`' and separated by commas '`,`'.
|
|
|
|
The Rust type of a Rhai array is `rhai::Array`.
|
|
|
|
[`type_of()`] an array returns `"array"`.
|
|
|
|
Arrays are disabled via the [`no_index`] feature.
|
|
|
|
The following functions (defined in the standard library but excluded if [`no_stdlib`]) operate on arrays:
|
|
|
|
| Function | Description |
|
|
| ---------- | ------------------------------------------------------------------------------------- |
|
|
| `push` | inserts an element at the end |
|
|
| `pop` | removes the last element and returns it ([`()`] if empty) |
|
|
| `shift` | removes the first element and returns it ([`()`] if empty) |
|
|
| `len` | returns the number of elements |
|
|
| `pad` | pads the array with an element until a specified length |
|
|
| `clear` | empties the array |
|
|
| `truncate` | cuts off the array at exactly a specified length (discarding all subsequent elements) |
|
|
|
|
Examples:
|
|
|
|
```rust
|
|
let y = [1, 2, 3]; // array literal with 3 elements
|
|
y[1] = 42;
|
|
|
|
print(y[1]); // prints 42
|
|
|
|
ts.list = y; // arrays can be assigned completely (by value copy)
|
|
let foo = ts.list[1];
|
|
foo == 42;
|
|
|
|
let foo = [1, 2, 3][0];
|
|
foo == 1;
|
|
|
|
fn abc() {
|
|
[42, 43, 44] // a function returning an array
|
|
}
|
|
|
|
let foo = abc()[0];
|
|
foo == 42;
|
|
|
|
let foo = y[0];
|
|
foo == 1;
|
|
|
|
y.push(4); // 4 elements
|
|
y.push(5); // 5 elements
|
|
|
|
print(y.len()); // prints 5
|
|
|
|
let first = y.shift(); // remove the first element, 4 elements remaining
|
|
first == 1;
|
|
|
|
let last = y.pop(); // remove the last element, 3 elements remaining
|
|
last == 5;
|
|
|
|
print(y.len()); // prints 3
|
|
|
|
y.pad(10, "hello"); // pad the array up to 10 elements
|
|
|
|
print(y.len()); // prints 10
|
|
|
|
y.truncate(5); // truncate the array to 5 elements
|
|
|
|
print(y.len()); // prints 5
|
|
|
|
y.clear(); // empty the array
|
|
|
|
print(y.len()); // prints 0
|
|
```
|
|
|
|
`push` and `pad` are only defined for standard built-in types. For custom types, type-specific versions must be registered:
|
|
|
|
```rust
|
|
engine.register_fn("push", |list: &mut Array, item: MyType| list.push(Box::new(item)) );
|
|
```
|
|
|
|
Object maps
|
|
-----------
|
|
|
|
Object maps are dictionaries. Properties of any type (`Dynamic`) can be freely added and retrieved.
|
|
Object map literals are built within braces '`#{`' ... '`}`' (_name_ `:` _value_ syntax similar to Rust)
|
|
and separated by commas '`,`'. The property _name_ can be a simple variable name following the same
|
|
naming rules as [variables], or an arbitrary string literal.
|
|
|
|
Property values can be accessed via the dot notation (_object_ `.` _property_) or index notation (_object_ `[` _property_ `]`).
|
|
The dot notation allows only property names that follow the same naming rules as [variables].
|
|
The index notation allows setting/getting properties of arbitrary names (even the empty string).
|
|
|
|
**Important:** Trying to read a non-existent property returns `()` instead of causing an error.
|
|
|
|
The Rust type of a Rhai object map is `rhai::Map`.
|
|
|
|
[`type_of()`] an object map returns `"map"`.
|
|
|
|
Object maps are disabled via the [`no_object`] feature.
|
|
|
|
The following functions (defined in the standard library but excluded if [`no_stdlib`]) operate on object maps:
|
|
|
|
| Function | Description |
|
|
| -------- | ------------------------------------------------------------ |
|
|
| `has` | does the object map contain a property of a particular name? |
|
|
| `len` | returns the number of properties |
|
|
| `clear` | empties the object map |
|
|
|
|
Examples:
|
|
|
|
```rust
|
|
let y = #{ // object map literal with 3 properties
|
|
a: 1,
|
|
bar: "hello",
|
|
"baz!$@": 123.456, // like JS, you can use any string as property names...
|
|
"": false, // even the empty string!
|
|
|
|
a: 42 // <- syntax error: duplicated property name
|
|
};
|
|
|
|
y.a = 42; // access via dot notation
|
|
y.baz!$@ = 42; // <- syntax error: only proper variable names allowed in dot notation
|
|
y."baz!$@" = 42; // <- syntax error: strings not allowed in dot notation
|
|
|
|
print(y.a); // prints 42
|
|
|
|
print(y["baz!$@"]); // prints 123.456 - access via index notation
|
|
|
|
ts.obj = y; // object maps can be assigned completely (by value copy)
|
|
let foo = ts.list.a;
|
|
foo == 42;
|
|
|
|
let foo = #{ a:1, b:2, c:3 }["a"];
|
|
foo == 1;
|
|
|
|
fn abc() {
|
|
#{ a:1, b:2, c:3 } // a function returning an object map
|
|
}
|
|
|
|
let foo = abc().b;
|
|
foo == 2;
|
|
|
|
let foo = y["a"];
|
|
foo == 42;
|
|
|
|
y.has("a") == true;
|
|
y.has("xyz") == false;
|
|
|
|
y.xyz == (); // A non-existing property returns '()'
|
|
y["xyz"] == ();
|
|
|
|
print(y.len()); // prints 3
|
|
|
|
y.clear(); // empty the object map
|
|
|
|
print(y.len()); // prints 0
|
|
```
|
|
|
|
Comparison operators
|
|
--------------------
|
|
|
|
Comparing most values of the same data type work out-of-the-box for standard types supported by the system.
|
|
|
|
However, if the [`no_stdlib`] feature is turned on, comparisons can only be made between restricted system
|
|
types - `INT` (`i64` or `i32` depending on [`only_i32`] and [`only_i64`]), `f64` (if not [`no_float`]), string, array, `bool`, `char`.
|
|
|
|
```rust
|
|
42 == 42; // true
|
|
42 > 42; // false
|
|
"hello" > "foo"; // true
|
|
"42" == 42; // false
|
|
```
|
|
|
|
Comparing two values of _different_ data types, or of unknown data types, always results in `false`.
|
|
|
|
```rust
|
|
42 == 42.0; // false - i64 is different from f64
|
|
42 > "42"; // false - i64 is different from string
|
|
42 <= "42"; // false again
|
|
|
|
let ts = new_ts(); // custom type
|
|
ts == 42; // false - types are not the same
|
|
```
|
|
|
|
Boolean operators
|
|
-----------------
|
|
|
|
| Operator | Description |
|
|
| -------- | ------------------------------- |
|
|
| `!` | Boolean _Not_ |
|
|
| `&&` | Boolean _And_ (short-circuits) |
|
|
| `\|\|` | Boolean _Or_ (short-circuits) |
|
|
| `&` | Boolean _And_ (full evaluation) |
|
|
| `\|` | Boolean _Or_ (full evaluation) |
|
|
|
|
Double boolean operators `&&` and `||` _short-circuit_, meaning that the second operand will not be evaluated
|
|
if the first one already proves the condition wrong.
|
|
|
|
Single boolean operators `&` and `|` always evaluate both operands.
|
|
|
|
```rust
|
|
this() || that(); // that() is not evaluated if this() is true
|
|
this() && that(); // that() is not evaluated if this() is false
|
|
|
|
this() | that(); // both this() and that() are evaluated
|
|
this() & that(); // both this() and that() are evaluated
|
|
```
|
|
|
|
Compound assignment operators
|
|
----------------------------
|
|
|
|
```rust
|
|
let number = 5;
|
|
number += 4; // number = number + 4
|
|
number -= 3; // number = number - 3
|
|
number *= 2; // number = number * 2
|
|
number /= 1; // number = number / 1
|
|
number %= 3; // number = number % 3
|
|
number <<= 2; // number = number << 2
|
|
number >>= 1; // number = number >> 1
|
|
```
|
|
|
|
The `+=` operator can also be used to build strings:
|
|
|
|
```rust
|
|
let my_str = "abc";
|
|
my_str += "ABC";
|
|
my_str += 12345;
|
|
|
|
my_str == "abcABC12345"
|
|
```
|
|
|
|
`if` statements
|
|
---------------
|
|
|
|
```rust
|
|
if foo(x) {
|
|
print("It's true!");
|
|
} else if bar == baz {
|
|
print("It's true again!");
|
|
} else if ... {
|
|
:
|
|
} else if ... {
|
|
:
|
|
} else {
|
|
print("It's finally false!");
|
|
}
|
|
```
|
|
|
|
All branches of an `if` statement must be enclosed within braces '`{`' .. '`}`', even when there is only one statement.
|
|
Like Rust, there is no ambiguity regarding which `if` clause a statement belongs to.
|
|
|
|
```rust
|
|
if (decision) print("I've decided!");
|
|
// ^ syntax error, expecting '{' in statement block
|
|
```
|
|
|
|
Like Rust, `if` statements can also be used as _expressions_, replacing the `? :` conditional operators in other C-like languages.
|
|
|
|
```rust
|
|
let x = 1 + if true { 42 } else { 123 } / 2;
|
|
x == 22;
|
|
|
|
let x = if false { 42 }; // No else branch defaults to '()'
|
|
x == ();
|
|
```
|
|
|
|
`while` loops
|
|
-------------
|
|
|
|
```rust
|
|
let x = 10;
|
|
|
|
while x > 0 {
|
|
print(x);
|
|
if x == 5 { break; } // break out of while loop
|
|
x = x - 1;
|
|
}
|
|
```
|
|
|
|
Infinite `loop`
|
|
---------------
|
|
|
|
```rust
|
|
let x = 10;
|
|
|
|
loop {
|
|
print(x);
|
|
x = x - 1;
|
|
if x == 0 { break; } // break out of loop
|
|
}
|
|
```
|
|
|
|
`for` loops
|
|
-----------
|
|
|
|
Iterating through a range or an array is provided by the `for` ... `in` loop.
|
|
|
|
```rust
|
|
let array = [1, 3, 5, 7, 9, 42];
|
|
|
|
// Iterate through array
|
|
for x in array {
|
|
print(x);
|
|
if x == 42 { break; }
|
|
}
|
|
|
|
// The 'range' function allows iterating from first to last-1
|
|
for x in range(0, 50) {
|
|
print(x);
|
|
if x == 42 { break; }
|
|
}
|
|
```
|
|
|
|
`return`-ing values
|
|
-------------------
|
|
|
|
```rust
|
|
return; // equivalent to return ();
|
|
|
|
return 123 + 456; // returns 579
|
|
```
|
|
|
|
Errors and `throw`-ing exceptions
|
|
--------------------------------
|
|
|
|
All of [`Engine`]'s evaluation/consuming methods return `Result<T, rhai::EvalAltResult>` with `EvalAltResult` holding error information.
|
|
To deliberately return an error during an evaluation, use the `throw` keyword.
|
|
|
|
```rust
|
|
if some_bad_condition_has_happened {
|
|
throw error; // 'throw' takes a string as the exception text
|
|
}
|
|
|
|
throw; // defaults to empty exception text: ""
|
|
```
|
|
|
|
Exceptions thrown via `throw` in the script can be captured by matching `Err(EvalAltResult::ErrorRuntime(`_reason_`, `_position_`))`
|
|
with the exception text captured by the first parameter.
|
|
|
|
```rust
|
|
let result = engine.eval::<i64>(r#"
|
|
let x = 42;
|
|
|
|
if x > 0 {
|
|
throw x + " is too large!";
|
|
}
|
|
"#);
|
|
|
|
println!(result); // prints "Runtime error: 42 is too large! (line 5, position 15)"
|
|
```
|
|
|
|
Functions
|
|
---------
|
|
|
|
Rhai supports defining functions in script (unless disabled with [`no_function`]):
|
|
|
|
```rust
|
|
fn add(x, y) {
|
|
return x + y;
|
|
}
|
|
|
|
print(add(2, 3));
|
|
```
|
|
|
|
### Implicit return
|
|
|
|
Just like in Rust, an implicit return can be used. In fact, the last statement of a block is _always_ the block's return value
|
|
regardless of whether it is terminated with a semicolon `';'`. This is different from Rust.
|
|
|
|
```rust
|
|
fn add(x, y) { // implicit return:
|
|
x + y; // value of the last statement (no need for ending semicolon)
|
|
// is used as the return value
|
|
}
|
|
|
|
fn add2(x) {
|
|
return x + 2; // explicit return
|
|
}
|
|
|
|
print(add(2, 3)); // prints 5
|
|
print(add2(42)); // prints 44
|
|
```
|
|
|
|
### No access to external scope
|
|
|
|
Functions can only access their parameters. They cannot access external variables (even _global_ variables).
|
|
|
|
```rust
|
|
let x = 42;
|
|
|
|
fn foo() { x } // <- syntax error: variable 'x' doesn't exist
|
|
```
|
|
|
|
### Passing arguments by value
|
|
|
|
Functions defined in script always take [`Dynamic`] parameters (i.e. the parameter can be of any type).
|
|
It is important to remember that all arguments are passed by _value_, so all functions are _pure_ (i.e. they never modify their arguments).
|
|
Any update to an argument will **not** be reflected back to the caller. This can introduce subtle bugs, if not careful.
|
|
|
|
```rust
|
|
fn change(s) { // 's' is passed by value
|
|
s = 42; // only a COPY of 's' is changed
|
|
}
|
|
|
|
let x = 500;
|
|
x.change(); // de-sugars to change(x)
|
|
x == 500; // 'x' is NOT changed!
|
|
```
|
|
|
|
### Global definitions only
|
|
|
|
Functions can only be defined at the global level, never inside a block or another function.
|
|
|
|
```rust
|
|
// Global level is OK
|
|
fn add(x, y) {
|
|
x + y
|
|
}
|
|
|
|
// The following will not compile
|
|
fn do_addition(x) {
|
|
fn add_y(n) { // functions cannot be defined inside another function
|
|
n + y
|
|
}
|
|
|
|
add_y(x)
|
|
}
|
|
```
|
|
|
|
### Functions overloading
|
|
|
|
Functions can be _overloaded_ and are resolved purely upon the function's _name_ and the _number_ of parameters
|
|
(but not parameter _types_, since all parameters are the same type - [`Dynamic`]).
|
|
New definitions _overwrite_ previous definitions of the same name and number of parameters.
|
|
|
|
```rust
|
|
fn foo(x,y,z) { print("Three!!! " + x + "," + y + "," + z) }
|
|
fn foo(x) { print("One! " + x) }
|
|
fn foo(x,y) { print("Two! " + x + "," + y) }
|
|
fn foo() { print("None.") }
|
|
fn foo(x) { print("HA! NEW ONE! " + x) } // overwrites previous definition
|
|
|
|
foo(1,2,3); // prints "Three!!! 1,2,3"
|
|
foo(42); // prints "HA! NEW ONE! 42"
|
|
foo(1,2); // prints "Two!! 1,2"
|
|
foo(); // prints "None."
|
|
```
|
|
|
|
Members and methods
|
|
-------------------
|
|
|
|
Properties and methods in a Rust custom type registered with the [`Engine`] can be called just like in Rust.
|
|
|
|
```rust
|
|
let a = new_ts(); // constructor function
|
|
a.field = 500; // property access
|
|
a.update(); // method call
|
|
|
|
update(a); // this works, but 'a' is unchanged because only
|
|
// a COPY of 'a' is passed to 'update' by VALUE
|
|
```
|
|
|
|
Custom types, properties and methods can be disabled via the [`no_object`] feature.
|
|
|
|
`print` and `debug`
|
|
-------------------
|
|
|
|
The `print` and `debug` functions default to printing to `stdout`, with `debug` using standard debug formatting.
|
|
|
|
```rust
|
|
print("hello"); // prints hello to stdout
|
|
print(1 + 2 + 3); // prints 6 to stdout
|
|
print("hello" + 42); // prints hello42 to stdout
|
|
debug("world!"); // prints "world!" to stdout using debug formatting
|
|
```
|
|
|
|
### Overriding `print` and `debug` with callback functions
|
|
|
|
When embedding Rhai into an application, it is usually necessary to trap `print` and `debug` output
|
|
(for logging into a tracking log, for example).
|
|
|
|
```rust
|
|
// Any function or closure that takes an &str argument can be used to override
|
|
// print and debug
|
|
engine.on_print(|x| println!("hello: {}", x));
|
|
engine.on_debug(|x| println!("DEBUG: {}", x));
|
|
|
|
// Example: quick-'n-dirty logging
|
|
let mut log: Vec<String> = Vec::new();
|
|
|
|
// Redirect print/debug output to 'log'
|
|
engine.on_print(|s| log.push(format!("entry: {}", s)));
|
|
engine.on_debug(|s| log.push(format!("DEBUG: {}", s)));
|
|
|
|
// Evaluate script
|
|
engine.eval::<()>(script)?;
|
|
|
|
// 'log' captures all the 'print' and 'debug' output
|
|
for entry in log {
|
|
println!("{}", entry);
|
|
}
|
|
```
|
|
|
|
Script optimization
|
|
===================
|
|
|
|
Rhai includes an _optimizer_ that tries to optimize a script after parsing.
|
|
This can reduce resource utilization and increase execution speed.
|
|
Script optimization can be turned off via the [`no_optimize`] feature.
|
|
|
|
For example, in the following:
|
|
|
|
```rust
|
|
{
|
|
let x = 999; // NOT eliminated: Rhai doesn't check yet whether a variable is used later on
|
|
123; // eliminated: no effect
|
|
"hello"; // eliminated: no effect
|
|
[1, 2, x, x*2, 5]; // eliminated: no effect
|
|
foo(42); // NOT eliminated: the function 'foo' may have side effects
|
|
666 // NOT eliminated: this is the return value of the block,
|
|
// and the block is the last one so this is the return value of the whole script
|
|
}
|
|
```
|
|
|
|
Rhai attempts to eliminate _dead code_ (i.e. code that does nothing, for example an expression by itself as a statement, which is allowed in Rhai).
|
|
The above script optimizes to:
|
|
|
|
```rust
|
|
{
|
|
let x = 999;
|
|
foo(42);
|
|
666
|
|
}
|
|
```
|
|
|
|
Constants propagation is used to remove dead code:
|
|
|
|
```rust
|
|
const ABC = true;
|
|
if ABC || some_work() { print("done!"); } // 'ABC' is constant so it is replaced by 'true'...
|
|
if true || some_work() { print("done!"); } // since '||' short-circuits, 'some_work' is never called
|
|
if true { print("done!"); } // <- the line above is equivalent to this
|
|
print("done!"); // <- the line above is further simplified to this
|
|
// because the condition is always true
|
|
```
|
|
|
|
These are quite effective for template-based machine-generated scripts where certain constant values
|
|
are spliced into the script text in order to turn on/off certain sections.
|
|
For fixed script texts, the constant values can be provided in a user-defined [`Scope`] object
|
|
to the [`Engine`] for use in compilation and evaluation.
|
|
|
|
Beware, however, that most operators are actually function calls, and those functions can be overridden,
|
|
so they are not optimized away:
|
|
|
|
```rust
|
|
const DECISION = 1;
|
|
|
|
if DECISION == 1 { // NOT optimized away because you can define
|
|
: // your own '==' function to override the built-in default!
|
|
:
|
|
} else if DECISION == 2 { // same here, NOT optimized away
|
|
:
|
|
} else if DECISION == 3 { // same here, NOT optimized away
|
|
:
|
|
} else {
|
|
:
|
|
}
|
|
```
|
|
|
|
because no operator functions will be run (in order not to trigger side effects) during the optimization process
|
|
(unless the optimization level is set to [`OptimizationLevel::Full`]). So, instead, do this:
|
|
|
|
```rust
|
|
const DECISION_1 = true;
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|
const DECISION_2 = false;
|
|
const DECISION_3 = false;
|
|
|
|
if DECISION_1 {
|
|
: // this branch is kept and promoted to the parent level
|
|
} else if DECISION_2 {
|
|
: // this branch is eliminated
|
|
} else if DECISION_3 {
|
|
: // this branch is eliminated
|
|
} else {
|
|
: // this branch is eliminated
|
|
}
|
|
```
|
|
|
|
In general, boolean constants are most effective for the optimizer to automatically prune
|
|
large `if`-`else` branches because they do not depend on operators.
|
|
|
|
Alternatively, turn the optimizer to [`OptimizationLevel::Full`]
|
|
|
|
Here be dragons!
|
|
================
|
|
|
|
Optimization levels
|
|
-------------------
|
|
|
|
[`OptimizationLevel::Full`]: #optimization-levels
|
|
[`OptimizationLevel::Simple`]: #optimization-levels
|
|
[`OptimizationLevel::None`]: #optimization-levels
|
|
|
|
There are actually three levels of optimizations: `None`, `Simple` and `Full`.
|
|
|
|
* `None` is obvious - no optimization on the AST is performed.
|
|
|
|
* `Simple` (default) performs relatively _safe_ optimizations without causing side effects
|
|
(i.e. it only relies on static analysis and will not actually perform any function calls).
|
|
|
|
* `Full` is _much_ more aggressive, _including_ running functions on constant arguments to determine their result.
|
|
One benefit to this is that many more optimization opportunities arise, especially with regards to comparison operators.
|
|
|
|
An [`Engine`]'s optimization level is set via a call to `set_optimization_level`:
|
|
|
|
```rust
|
|
// Turn on aggressive optimizations
|
|
engine.set_optimization_level(rhai::OptimizationLevel::Full);
|
|
```
|
|
|
|
When the optimization level is [`OptimizationLevel::Full`], the [`Engine`] assumes all functions to be _pure_ and will _eagerly_
|
|
evaluated all function calls with constant arguments, using the result to replace the call. This also applies to all operators
|
|
(which are implemented as functions). For instance, the same example above:
|
|
|
|
```rust
|
|
// When compiling the following with OptimizationLevel::Full...
|
|
|
|
const DECISION = 1;
|
|
// this condition is now eliminated because 'DECISION == 1'
|
|
if DECISION == 1 { // is a function call to the '==' function, and it returns 'true'
|
|
print("hello!"); // this block is promoted to the parent level
|
|
} else {
|
|
print("boo!"); // this block is eliminated because it is never reached
|
|
}
|
|
|
|
print("hello!"); // <- the above is equivalent to this
|
|
// ('print' and 'debug' are handled specially)
|
|
```
|
|
|
|
Because of the eager evaluation of functions, many constant expressions will be evaluated and replaced by the result.
|
|
This does not happen with [`OptimizationLevel::Simple`] which doesn't assume all functions to be _pure_.
|
|
|
|
```rust
|
|
// When compiling the following with OptimizationLevel::Full...
|
|
|
|
let x = (1+2)*3-4/5%6; // <- will be replaced by 'let x = 9'
|
|
let y = (1>2) || (3<=4); // <- will be replaced by 'let y = true'
|
|
```
|
|
|
|
Function side effect considerations
|
|
----------------------------------
|
|
|
|
All of Rhai's built-in functions (and operators which are implemented as functions) are _pure_ (i.e. they do not mutate state
|
|
nor cause side any effects, with the exception of `print` and `debug` which are handled specially) so using [`OptimizationLevel::Full`]
|
|
is usually quite safe _unless_ you register your own types and functions.
|
|
|
|
If custom functions are registered, they _may_ be called (or maybe not, if the calls happen to lie within a pruned code block).
|
|
If custom functions are registered to replace built-in operators, they will also be called when the operators are used (in an `if`
|
|
statement, for example) and cause side-effects.
|
|
|
|
Function volatility considerations
|
|
---------------------------------
|
|
|
|
Even if a custom function does not mutate state nor cause side effects, it may still be _volatile_, i.e. it _depends_ on the external
|
|
environment and not _pure_. A perfect example is a function that gets the current time - obviously each run will return a different value!
|
|
The optimizer, when using [`OptimizationLevel::Full`], _assumes_ that all functions are _pure_, so when it finds constant arguments
|
|
it will eagerly run execute the function call. This causes the script to behave differently from the intended semantics because
|
|
essentially the result of the function call will always be the same value.
|
|
|
|
Therefore, **avoid using [`OptimizationLevel::Full`]** if you intend to register non-_pure_ custom types and/or functions.
|
|
|
|
Subtle semantic changes
|
|
-----------------------
|
|
|
|
Some optimizations can alter subtle semantics of the script. For example:
|
|
|
|
```rust
|
|
if true { // condition always true
|
|
123.456; // eliminated
|
|
hello; // eliminated, EVEN THOUGH the variable doesn't exist!
|
|
foo(42) // promoted up-level
|
|
}
|
|
|
|
foo(42) // <- the above optimizes to this
|
|
```
|
|
|
|
Nevertheless, if the original script were evaluated instead, it would have been an error - the variable `hello` doesn't exist,
|
|
so the script would have been terminated at that point with an error return.
|
|
|
|
In fact, any errors inside a statement that has been eliminated will silently _disappear_:
|
|
|
|
```rust
|
|
print("start!");
|
|
if my_decision { /* do nothing... */ } // eliminated due to no effect
|
|
print("end!");
|
|
|
|
// The above optimizes to:
|
|
|
|
print("start!");
|
|
print("end!");
|
|
```
|
|
|
|
In the script above, if `my_decision` holds anything other than a boolean value, the script should have been terminated due to a type error.
|
|
However, after optimization, the entire `if` statement is removed (because an access to `my_decision` produces no side effects),
|
|
thus the script silently runs to completion without errors.
|
|
|
|
Turning off optimizations
|
|
-------------------------
|
|
|
|
It is usually a bad idea to depend on a script failing or such kind of subtleties, but if it turns out to be necessary (why? I would never guess),
|
|
turn it off by setting the optimization level to [`OptimizationLevel::None`].
|
|
|
|
```rust
|
|
let engine = rhai::Engine::new();
|
|
|
|
// Turn off the optimizer
|
|
engine.set_optimization_level(rhai::OptimizationLevel::None);
|
|
```
|
|
|
|
`eval` - or "How to Shoot Yourself in the Foot even Easier"
|
|
---------------------------------------------------------
|
|
|
|
Saving the best for last: in addition to script optimizations, there is the ever-dreaded... `eval` function!
|
|
|
|
```rust
|
|
let x = 10;
|
|
|
|
fn foo(x) { x += 12; x }
|
|
|
|
let script = "let y = x;"; // build a script
|
|
script += "y += foo(y);";
|
|
script += "x + y";
|
|
|
|
let result = eval(script); // <- look, JS, we can also do this!
|
|
|
|
print("Answer: " + result); // prints 42
|
|
|
|
print("x = " + x); // prints 10: functions call arguments are passed by value
|
|
print("y = " + y); // prints 32: variables defined in 'eval' persist!
|
|
|
|
eval("{ let z = y }"); // to keep a variable local, use a statement block
|
|
|
|
print("z = " + z); // <- error: variable 'z' not found
|
|
|
|
"print(42)".eval(); // <- nope... just like 'type_of', method-call style doesn't work
|
|
```
|
|
|
|
Script segments passed to `eval` execute inside the current [`Scope`], so they can access and modify _everything_,
|
|
including all variables that are visible at that position in code! It is almost as if the script segments were
|
|
physically pasted in at the position of the `eval` call.
|
|
|
|
```rust
|
|
let script = "x += 32";
|
|
let x = 10;
|
|
eval(script); // variable 'x' in the current scope is visible!
|
|
print(x); // prints 42
|
|
|
|
// The above is equivalent to:
|
|
let script = "x += 32";
|
|
let x = 10;
|
|
x += 32;
|
|
print(x);
|
|
```
|
|
|
|
For those who subscribe to the (very sensible) motto of ["`eval` is **evil**"](http://linterrors.com/js/eval-is-evil),
|
|
disable `eval` by overriding it, probably with something that throws.
|
|
|
|
```rust
|
|
fn eval(script) { throw "eval is evil! I refuse to run " + script }
|
|
|
|
let x = eval("40 + 2"); // 'eval' here throws "eval is evil! I refuse to run 40 + 2"
|
|
```
|
|
|
|
Or override it from Rust:
|
|
|
|
```rust
|
|
fn alt_eval(script: String) -> Result<(), EvalAltResult> {
|
|
Err(format!("eval is evil! I refuse to run {}", script).into())
|
|
}
|
|
|
|
engine.register_result_fn("eval", alt_eval);
|
|
```
|