57 lines
1.8 KiB
Markdown
57 lines
1.8 KiB
Markdown
|
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)"
|
||
|
|
```
|