Closure

Rust closures can be passed to PHP through a wrapper class PhpClosure. The Rust closure must be static (i.e. can only reference things with a 'static lifetime, so not self in methods), and can take up to 8 parameters, all of which must implement FromZval. The return type must implement IntoZval.

Passing closures from Rust to PHP is feature-gated behind the closure feature. Enable it in your Cargo.toml:

ext-php-rs = { version = "...", features = ["closure"] }

PHP callables (which includes closures) can be passed to Rust through the Callable type. When calling a callable, you must provide it with a Vec of arguments, all of which must implement IntoZval and Clone.

Internally, when you enable the closure feature, a class PhpClosure is registered alongside your other classes:

<?php

class PhpClosure
{
    public function __invoke(..$args): mixed;
}

This class cannot be instantiated from PHP. When the class is invoked, the underlying Rust closure is called. There are three types of closures in Rust:

Fn and FnMut

These closures can be called multiple times. FnMut differs from Fn in the fact that it can modify variables in its scope.

Example

#![cfg_attr(windows, feature(abi_vectorcall))]
extern crate ext_php_rs;
use ext_php_rs::prelude::*;

#[php_function]
pub fn closure_get_string() -> Closure {
    // Return a closure which takes two integers and returns a string
    Closure::wrap(Box::new(|a, b| {
        format!("A: {} B: {}", a, b)
    }) as Box<dyn Fn(i32, i32) -> String>)
}

#[php_function]
pub fn closure_count() -> Closure {
    let mut count = 0i32;

    // Return a closure which takes an integer, adds it to a persistent integer,
    // and returns the updated value.
    Closure::wrap(Box::new(move |a: i32| {
        count += a;
        count
    }) as Box<dyn FnMut(i32) -> i32>)
}
fn main() {}

FnOnce

Closures that implement FnOnce can only be called once. They consume some sort of value. Calling these closures more than once will cause them to throw an exception. They must be wrapped using the wrap_once function instead of wrap.

Internally, the FnOnce closure is wrapped again by an FnMut closure, which owns the FnOnce closure until it is called. If the FnMut closure is called again, the FnOnce closure would have already been consumed, and an exception will be thrown.

Example

#![cfg_attr(windows, feature(abi_vectorcall))]
extern crate ext_php_rs;
use ext_php_rs::prelude::*;

#[php_function]
pub fn closure_return_string() -> Closure {
    let example: String = "Hello, world!".into();

    // This closure consumes `example` and therefore cannot be called more than once.
    Closure::wrap_once(Box::new(move || {
        example
    }) as Box<dyn FnOnce() -> String>)
}
fn main() {}

Closures must be boxed as PHP classes cannot support generics, therefore trait objects must be used. These must be boxed to have a compile time size.

Callable

Callables are simply represented as zvals. You can attempt to get a callable function by its name, or as a parameter. They can be called through the try_call method implemented on Callable, which returns a zval in a result.

Callable parameter

#![cfg_attr(windows, feature(abi_vectorcall))]
extern crate ext_php_rs;
use ext_php_rs::prelude::*;

#[php_function]
pub fn callable_parameter(call: ZendCallable) {
    let val = call.try_call(vec![&0, &1, &"Hello"]).expect("Failed to call function");
    dbg!(val);
}
fn main() {}

Named Arguments (PHP 8.0+)

You can call PHP functions with named arguments using try_call_named or try_call_with_named. Named arguments allow you to pass parameters by name rather than position, which is especially useful when dealing with functions that have many optional parameters.

#![cfg_attr(windows, feature(abi_vectorcall))]
extern crate ext_php_rs;
use ext_php_rs::prelude::*;
use ext_php_rs::call_user_func_named;

#[php_function]
pub fn call_with_named_args() -> String {
    // Get str_replace function
    let str_replace = ZendCallable::try_from_name("str_replace")
        .expect("str_replace not found");

    // Call with named arguments in any order
    let result = str_replace.try_call_named(&[
        ("subject", &"Hello world"),
        ("search", &"world"),
        ("replace", &"PHP"),
    ]).expect("Failed to call str_replace");

    result.string().unwrap_or_default()
}

#[php_function]
pub fn call_with_mixed_args(callback: ZendCallable) {
    // Mix positional and named arguments
    let result = callback.try_call_with_named(
        &[&"positional_arg"],  // positional args first
        &[("named", &"named_value")],  // then named args
    ).expect("Failed to call function");
    dbg!(result);
}
fn main() {}

There’s also a convenient call_user_func_named! macro:

// Named arguments only
call_user_func_named!(callable, arg1: value1, arg2: value2)?;

// Positional arguments followed by named arguments
call_user_func_named!(callable, [pos1, pos2], named1: val1, named2: val2)?;