New register_raw_fn_n shortcuts.
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Stephen Chung
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127
doc/src/rust/register-raw.md
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127
doc/src/rust/register-raw.md
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Use the Low-Level API to Register a Rust Function
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================================================
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{{#include ../links.md}}
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When a native Rust function is registered with an `Engine` using the `Engine::register_XXX` API,
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Rhai transparently converts all function arguments from [`Dynamic`] into the correct types before
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calling the function.
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For more power and flexibility, there is a _low-level_ API to work directly with [`Dynamic`] values
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without the conversions.
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Raw Function Registration
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-------------------------
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The `Engine::register_raw_fn` method is marked _volatile_, meaning that it may be changed without warning.
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If this is acceptable, then using this method to register a Rust function opens up more opportunities.
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In particular, a reference to the current `Engine` instance is passed as an argument so the Rust function
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can also use `Engine` facilities (like evaluating a script).
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```rust
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engine.register_raw_fn(
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"increment_by", // function name
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&[ // a slice containing parameter types
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std::any::TypeId::of::<i64>(), // type of first parameter
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std::any::TypeId::of::<i64>() // type of second parameter
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],
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|engine: &Engine, lib: &Module, args: &mut [&mut Dynamic]| { // fixed function signature
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// Arguments are guaranteed to be correct in number and of the correct types.
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// But remember this is Rust, so you can keep only one mutable reference at any one time!
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// Therefore, get a '&mut' reference to the first argument _last_.
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// Alternatively, use `args.split_at_mut(1)` etc. to split the slice first.
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let y: i64 = *args[1].downcast_ref::<i64>() // get a reference to the second argument
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.unwrap(); // then copying it because it is a primary type
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let y: i64 = std::mem::take(args[1]).cast::<i64>(); // alternatively, directly 'consume' it
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let x: &mut i64 = args[0].downcast_mut::<i64>() // get a '&mut' reference to the
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.unwrap(); // first argument
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*x += y; // perform the action
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Ok(().into()) // must be 'Result<Dynamic, Box<EvalAltResult>>'
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}
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);
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// The above is the same as (in fact, internally they are equivalent):
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engine.register_fn("increment_by", |x: &mut i64, y: i64| x += y);
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```
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Shortcuts
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---------
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As usual with Rhai, there are shortcuts. For functions of zero to four parameters, which should be
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the majority, use one of the `Engine::register_raw_fn_n` (where `n = 0..4`) methods:
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```rust
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// Specify parameter types as generics
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engine.register_raw_fn_2::<i64, i64>(
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"increment_by",
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|engine: &Engine, lib: &Module, args: &mut [&mut Dynamic]| { ... }
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);
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```
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Closure Signature
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-----------------
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The closure passed to `Engine::register_raw_fn` takes the following form:
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`Fn(engine: &Engine, lib: &Module, args: &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>> + 'static`
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where:
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* `engine` - a reference to the current [`Engine`], with all configurations and settings.
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* `lib` - a reference to the current collection of script-defined functions, as a [`Module`].
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* `args` - a reference to a slice containing `&mut` references to [`Dynamic`] values.
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The slice is guaranteed to contain enough arguments _of the correct types_.
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Remember, in Rhai, all arguments _except_ the _first_ one are always passed by _value_ (i.e. cloned).
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Therefore, it is unnecessary to ever mutate any argument except the first one, as all mutations
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will be on the cloned copy.
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Extract Arguments
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-----------------
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To extract an argument from the `args` parameter (`&mut [&mut Dynamic]`), use the following:
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| Argument type | Access (`n` = argument position) | Result |
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| ------------------------------ | -------------------------------------- | ---------------------------------------------------------- |
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| [Primary type][standard types] | `args[n].clone().cast::<T>()` | Copy of value. |
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| Custom type | `args[n].downcast_ref::<T>().unwrap()` | Immutable reference to value. |
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| Custom type (consumed) | `mem::take(args[n]).cast::<T>()` | The _consumed_ value.<br/>The original value becomes `()`. |
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| `this` object | `args[0].downcast_mut::<T>().unwrap()` | Mutable reference to value. |
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When there is a mutable reference to the `this` object (i.e. the first argument),
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there can be no other immutable references to `args`, otherwise the Rust borrow checker will complain.
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Hold Multiple References
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------------------------
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In order to access a value argument that is expensive to clone _while_ holding a mutable reference
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to the first argument, either _consume_ that argument via `mem::take` as above, or use `args.split_at`
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to partition the slice:
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```rust
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// Partition the slice
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let (first, rest) = args.split_at_mut(1);
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// Mutable reference to the first parameter
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let this_ptr = first[0].downcast_mut::<A>().unwrap();
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// Immutable reference to the second value parameter
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// This can be mutable but there is no point because the parameter is passed by value
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let value = rest[0].downcast_ref::<B>().unwrap();
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```
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171
src/api.rs
171
src/api.rs
@ -33,7 +33,7 @@ use crate::stdlib::{fs::File, io::prelude::*, path::PathBuf};
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/// Engine public API
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impl Engine {
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/// Register a function with the `Engine`.
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/// Register a function of the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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@ -52,7 +52,7 @@ impl Engine {
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pub fn register_raw_fn(
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&mut self,
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name: &str,
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args: &[TypeId],
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arg_types: &[TypeId],
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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@ -62,7 +62,172 @@ impl Engine {
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+ Sync
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+ 'static,
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) {
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self.global_module.set_fn_var_args(name, args, func);
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self.global_module.set_fn_var_args(name, arg_types, func);
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}
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/// Register a function of no parameters with the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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/// This function is very low level.
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#[deprecated(note = "this function is volatile and may change")]
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pub fn register_raw_fn_0(
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&mut self,
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name: &str,
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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#[cfg(feature = "sync")] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ Send
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+ Sync
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+ 'static,
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) {
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self.global_module.set_fn_var_args(name, &[], func);
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}
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/// Register a function of one parameter with the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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/// This function is very low level.
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///
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/// Arguments are simply passed in as a mutable array of `&mut Dynamic`.
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/// The argument is guaranteed to be of the correct type.
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///
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/// To get access to a primary parameter value (i.e. cloning is cheap), use: `args[n].clone().cast::<T>()`
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///
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/// To get access to a parameter value and avoid cloning, use `std::mem::take(args[n]).cast::<T>()`.
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/// Notice that this will _consume_ the argument, replacing it with `()`.
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///
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/// To get access to the first mutable parameter, use `args.get_mut(0).unwrap()`
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#[deprecated(note = "this function is volatile and may change")]
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pub fn register_raw_fn_1<A: Variant + Clone>(
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&mut self,
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name: &str,
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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#[cfg(feature = "sync")] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ Send
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+ Sync
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+ 'static,
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) {
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self.global_module
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.set_fn_var_args(name, &[TypeId::of::<A>()], func);
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}
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/// Register a function of two parameters with the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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/// This function is very low level.
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///
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/// Arguments are simply passed in as a mutable array of `&mut Dynamic`.
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/// The arguments are guaranteed to be of the correct types.
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///
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/// To get access to a primary parameter value (i.e. cloning is cheap), use: `args[n].clone().cast::<T>()`
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///
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/// To get access to a parameter value and avoid cloning, use `std::mem::take(args[n]).cast::<T>()`.
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/// Notice that this will _consume_ the argument, replacing it with `()`.
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///
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/// To get access to the first mutable parameter, use `args.get_mut(0).unwrap()`
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#[deprecated(note = "this function is volatile and may change")]
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pub fn register_raw_fn_2<A: Variant + Clone, B: Variant + Clone>(
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&mut self,
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name: &str,
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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#[cfg(feature = "sync")] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ Send
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+ Sync
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+ 'static,
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) {
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self.global_module
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.set_fn_var_args(name, &[TypeId::of::<A>(), TypeId::of::<B>()], func);
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}
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/// Register a function of three parameters with the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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/// This function is very low level.
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///
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/// Arguments are simply passed in as a mutable array of `&mut Dynamic`.
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/// The arguments are guaranteed to be of the correct types.
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///
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/// To get access to a primary parameter value (i.e. cloning is cheap), use: `args[n].clone().cast::<T>()`
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///
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/// To get access to a parameter value and avoid cloning, use `std::mem::take(args[n]).cast::<T>()`.
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/// Notice that this will _consume_ the argument, replacing it with `()`.
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///
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/// To get access to the first mutable parameter, use `args.get_mut(0).unwrap()`
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#[deprecated(note = "this function is volatile and may change")]
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pub fn register_raw_fn_3<A: Variant + Clone, B: Variant + Clone, C: Variant + Clone>(
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&mut self,
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name: &str,
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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#[cfg(feature = "sync")] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ Send
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+ Sync
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+ 'static,
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) {
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self.global_module.set_fn_var_args(
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name,
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&[TypeId::of::<A>(), TypeId::of::<B>(), TypeId::of::<C>()],
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func,
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);
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}
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/// Register a function of four parameters with the `Engine`.
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///
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/// ## WARNING - Low Level API
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///
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/// This function is very low level.
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///
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/// Arguments are simply passed in as a mutable array of `&mut Dynamic`.
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/// The arguments are guaranteed to be of the correct types.
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///
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/// To get access to a primary parameter value (i.e. cloning is cheap), use: `args[n].clone().cast::<T>()`
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///
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/// To get access to a parameter value and avoid cloning, use `std::mem::take(args[n]).cast::<T>()`.
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/// Notice that this will _consume_ the argument, replacing it with `()`.
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///
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/// To get access to the first mutable parameter, use `args.get_mut(0).unwrap()`
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#[deprecated(note = "this function is volatile and may change")]
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pub fn register_raw_fn_4<
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A: Variant + Clone,
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B: Variant + Clone,
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C: Variant + Clone,
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D: Variant + Clone,
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>(
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&mut self,
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name: &str,
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#[cfg(not(feature = "sync"))] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ 'static,
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#[cfg(feature = "sync")] func: impl Fn(&Engine, &Module, &mut [&mut Dynamic]) -> Result<Dynamic, Box<EvalAltResult>>
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+ Send
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+ Sync
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+ 'static,
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) {
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self.global_module.set_fn_var_args(
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name,
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&[
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TypeId::of::<A>(),
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TypeId::of::<B>(),
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TypeId::of::<C>(),
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TypeId::of::<D>(),
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],
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func,
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);
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}
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/// Register a custom type for use with the `Engine`.
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