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Implement function pointers.

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This commit is contained in:
Stephen Chung
2020-06-25 18:07:57 +08:00
parent aeb47efce8
commit fe640e0e13
18 changed files with 269 additions and 31 deletions
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1
doc/src/SUMMARY.md
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@@ -71,6 +71,7 @@ The Rhai Scripting Language
14. [Functions](language/functions.md)
1. [Function Overloading](language/overload.md)
2. [Call Method as Function](language/method.md)
3. [Function Pointers](language/fn-ptr.md)
15. [Print and Debug](language/print-debug.md)
16. [Modules](language/modules/index.md)
1. [Export Variables, Functions and Sub-Modules](language/modules/export.md)

2
doc/src/about/features.md
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@@ -35,6 +35,8 @@ Dynamic
* Organize code base with dynamically-loadable [modules].
* [Function pointers].
Safe
----

3
doc/src/about/non-design.md
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@@ -11,10 +11,13 @@ It doesn't attempt to be a new language. For example:
* No traits... so it is also not Rust. Do your Rusty stuff in Rust.
* No structures/records - define your types in Rust instead; Rhai can seamlessly work with _any Rust type_.
There is, however, a built-in [object map] type which is adequate for most uses.
* No first-class functions - Code your functions in Rust instead, and register them with Rhai.
There is, however, support for simple [function pointers] allowing runtime dispatch by function name.
* No garbage collection - this should be expected, so...
* No closures - do your closure magic in Rust instead; [turn a Rhai scripted function into a Rust closure]({{rootUrl}}/engine/call-fn.md).

2
doc/src/language/dynamic.md
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@@ -27,6 +27,8 @@ if type_of(mystery) == "i64" {
print("Hey, I got an array here!");
} else if type_of(mystery) == "map" {
print("Hey, I got an object map here!");
} else if type_of(mystery) == "Fn" {
print("Hey, I got a function pointer here!");
} else if type_of(mystery) == "TestStruct" {
print("Hey, I got the TestStruct custom type here!");
} else {

2
doc/src/language/eval.md
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@@ -28,7 +28,7 @@ eval("{ let z = y }"); // to keep a variable local, use a statement blo
print("z = " + z); // <- error: variable 'z' not found
"print(42)".eval(); // <- nope... method-call style doesn't work
"print(42)".eval(); // <- nope... method-call style doesn't work with 'eval'
```
Script segments passed to `eval` execute inside the current [`Scope`], so they can access and modify _everything_,

56
doc/src/language/fn-ptr.md Normal file
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@@ -0,0 +1,56 @@
Function Pointers
=================
It is possible to store a _function pointer_ in a variable just like a normal value.
In fact, internally a function pointer simply stores the _name_ of the function as a string.
Call a function pointer using the `call` method, which needs to be called in method-call style.
Built-in Functions
------------------
The following standard methods (mostly defined in the [`BasicFnPackage`]({{rootUrl}}/rust/packages.md) but excluded if
using a [raw `Engine`]) operate on [strings]:
| Function | Parameter(s) | Description |
| -------------------------- | ------------ | --------------------------------------------------------------------- |
| `name` method and property | _none_ | returns the name of the function encapsulated by the function pointer |
Examples
--------
```rust
fn foo(x) { 41 + x }
let func = Fn("foo"); // use the 'Fn' function to create a function pointer
print(func); // prints 'Fn(foo)'
let func = fn_name.Fn(); // <- error: 'Fn' cannot be called in method-call style
func.type_of() == "Fn"; // type_of() as function pointer is 'Fn'
func.name == "foo";
func.call(1) == 42; // call a function pointer with the 'call' method
foo(1) == 42; // <- the above de-sugars to this
call(func, 1); //<- error: 'call (Fn, i64)' is not a registered function
let len = Fn("len"); // 'Fn' also works with registered native Rust functions
len.call("hello") == 5;
let add = Fn("+"); // 'Fn' works with built-in operators also
add.call(40, 2) == 42;
let fn_name = "hello"; // the function name does not have to exist yet
let hello = Fn(fn_name + "_world");
hello.call(0); // error: function not found - "hello_world (i64)"
```

29
doc/src/language/values-and-types.md
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@@ -5,20 +5,21 @@ Values and Types
The following primitive types are supported natively:
| Category | Equivalent Rust types | [`type_of()`] | `to_string()` |
| --------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | --------------------- | --------------------- |
| **Integer number** | `u8`, `i8`, `u16`, `i16`, <br/>`u32`, `i32` (default for [`only_i32`]),<br/>`u64`, `i64` _(default)_ | `"i32"`, `"u64"` etc. | `"42"`, `"123"` etc. |
| **Floating-point number** (disabled with [`no_float`]) | `f32`, `f64` _(default)_ | `"f32"` or `"f64"` | `"123.4567"` etc. |
| **Boolean value** | `bool` | `"bool"` | `"true"` or `"false"` |
| **Unicode character** | `char` | `"char"` | `"A"`, `"x"` etc. |
| **Immutable Unicode string** | `rhai::ImmutableString` (implemented as `Rc<String>` or `Arc<String>`) | `"string"` | `"hello"` etc. |
| **Array** (disabled with [`no_index`]) | `rhai::Array` | `"array"` | `"[ ?, ?, ? ]"` |
| **Object map** (disabled with [`no_object`]) | `rhai::Map` | `"map"` | `#{ "a": 1, "b": 2 }` |
| **Timestamp** (implemented in the [`BasicTimePackage`]({{rootUrl}}/rust/packages.md), disabled with [`no_std`]) | `std::time::Instant` ([`instant::Instant`](https://crates.io/crates/instant) if not [WASM] build) | `"timestamp"` | _not supported_ |
| **Dynamic value** (i.e. can be anything) | `rhai::Dynamic` | _the actual type_ | _actual value_ |
| **System integer** (current configuration) | `rhai::INT` (`i32` or `i64`) | `"i32"` or `"i64"` | `"42"`, `"123"` etc. |
| **System floating-point** (current configuration, disabled with [`no_float`]) | `rhai::FLOAT` (`f32` or `f64`) | `"f32"` or `"f64"` | `"123.456"` etc. |
| **Nothing/void/nil/null/Unit** (or whatever it is called) | `()` | `"()"` | `""` _(empty string)_ |
| Category | Equivalent Rust types | [`type_of()`] | `to_string()` |
| ----------------------------------------------------------------------------------------------------------------- | ---------------------------------------------------------------------------------------------------- | --------------------- | ----------------------- |
| **Integer number** | `u8`, `i8`, `u16`, `i16`, <br/>`u32`, `i32` (default for [`only_i32`]),<br/>`u64`, `i64` _(default)_ | `"i32"`, `"u64"` etc. | `"42"`, `"123"` etc. |
| **Floating-point number** (disabled with [`no_float`]) | `f32`, `f64` _(default)_ | `"f32"` or `"f64"` | `"123.4567"` etc. |
| **Boolean value** | `bool` | `"bool"` | `"true"` or `"false"` |
| **Unicode character** | `char` | `"char"` | `"A"`, `"x"` etc. |
| **Immutable Unicode [string]** | `rhai::ImmutableString` (implemented as `Rc<String>` or `Arc<String>`) | `"string"` | `"hello"` etc. |
| **[`Array`]** (disabled with [`no_index`]) | `rhai::Array` | `"array"` | `"[ ?, ?, ? ]"` |
| **[Object map]** (disabled with [`no_object`]) | `rhai::Map` | `"map"` | `"#{ "a": 1, "b": 2 }"` |
| **[Timestamp]** (implemented in the [`BasicTimePackage`]({{rootUrl}}/rust/packages.md), disabled with [`no_std`]) | `std::time::Instant` ([`instant::Instant`](https://crates.io/crates/instant) if not [WASM] build) | `"timestamp"` | _not supported_ |
| **[Function pointer]** (disabled with [`no_function`]) | _None_ | `Fn` | `"Fn(foo)"` |
| **[`Dynamic`] value** (i.e. can be anything) | `rhai::Dynamic` | _the actual type_ | _actual value_ |
| **System integer** (current configuration) | `rhai::INT` (`i32` or `i64`) | `"i32"` or `"i64"` | `"42"`, `"123"` etc. |
| **System floating-point** (current configuration, disabled with [`no_float`]) | `rhai::FLOAT` (`f32` or `f64`) | `"f32"` or `"f64"` | `"123.456"` etc. |
| **Nothing/void/nil/null/Unit** (or whatever it is called) | `()` | `"()"` | `""` _(empty string)_ |
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.

2
doc/src/links.md
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@@ -65,6 +65,8 @@
[function]: {{rootUrl}}/language/functions.md
[functions]: {{rootUrl}}/language/functions.md
[function pointer]: {{rootUrl}}/language/fn-ptr.md
[function pointers]: {{rootUrl}}/language/fn-ptr.md
[`Module`]: {{rootUrl}}/language/modules/index.md
[module]: {{rootUrl}}/language/modules/index.md

1
doc/src/rust/packages/builtin.md
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@@ -18,6 +18,7 @@ Built-In Packages
| `BasicMathPackage` | Basic math functions (e.g. `sin`, `sqrt`) | No | Yes |
| `BasicArrayPackage` | Basic [array] functions (not available under `no_index`) | No | Yes |
| `BasicMapPackage` | Basic [object map] functions (not available under `no_object`) | No | Yes |
| `BasicFnPackage` | Basic methods for [function pointers]. | Yes | Yes |
| `EvalPackage` | Disable [`eval`] | No | No |
| `CorePackage` | Basic essentials | Yes | Yes |
| `StandardPackage` | Standard library (default for `Engine::new`) | No | Yes |