功能锈阵列 [英] Rust array of functions

问题描述

我是新来的锈，并试图做闭包的东西是微不足道的JavaScript中，巨蟒等，但我遇到鲁斯特终身的问题。我理解的错误消息，但它使我相信我想要做的是pretty难生锈。

I'm new to Rust and trying to do something with closures which is trivial in JavaScript, Python, etc. but I am running into lifetime issues in Rust. I understand the error message, but it leads me to believe what I want to do is pretty hard in Rust.

我只是想创建一个函数数组， A ，这样

I just want to create an array of functions, a, such that

• A [0] 在函数返回0


• A [1] 在函数返回1


• ...


• A [9] 在函数返回9

• a[0] is the function returning 0
• a[1] is the function returning 1
• ...
• a[9] is the function returning 9

我试过（ http://is.gd/mTycTC ）：

fn main() {
    let a : [||->uint,  ..10];
    for i in range(0u, 10) {
        a[i] = ||{i};
    }
    println!("{} {} {}", a[1](), a[5](), a[9]())
}

但我得到了一生的错误。该报告的错误是不能推断适当的寿命因相互矛盾的要求为功能 A ，因为寿命不能经受住了，而块，使封锁不能活得比自己的堆栈帧，这当然他们​​会因为我调用它们在的println！。

But I got a lifetime error. The reported error was "cannot infer an appropriate lifetime due to conflicting requirements" for the functions in a because the lifetimes cannot outlive the while block so that the closures cannot outlive their stack frame, which of course they would because I am invoking them in println!.

我敢肯定，必须有建立这个数组功能的一种方式，但如何？

I'm sure there must be a way to build up this array of functions, but how?

推荐答案

您需要使用移动|＆放大器;：| {I} 和＃！[功能（unboxed_closures）] 。

基本上，移动意味着这个关闭将采取 I 通过值而不是引用。默认情况下，关闭经常只需要引用，在你的情况下，它是被禁止的的一生中，我仅限于身体循环。

Basically, move implies that this closure will take i by value rather than by reference. By default the regular closures only take references, in your case it is forbidden as the lifetime of i is limited to the body loop.

您还需要添加＆放大器; ，它指定闭合类型为的 FN （你需要＆放大器; MUT： FnMut 和：的的 FnOnce ）。目前，一个普通的 || 仍然是一个古老的关闭，但它最终应该的代名词|＆放大器; MUT：| 。

You also need to add the &:, which specifies that the closure is of type Fn (you would need &mut: for FnMut and : for FnOnce). Currently a regular || is still an old closure, but it should eventually be a synonym of |&mut:|.

此外，铁锈会抱怨你的数组可能无法完全初始化。为了避免这个问题，你可以使用 VEC＆LT; _＆GT; ，或使用的std ::纪念品::初始化：

Also, Rust will complain that your array may not be fully initialized. To avoid it, you can either use a Vec<_>, or use std::mem::uninitialized:

#![feature(unboxed_closures)]

fn main() {
    // The `_` tells rust to infer the type by itself.
    let mut a : [_,  ..10] = unsafe{std::mem::uninitialized()};
    for i in range(0u, 10) {
        a[i] = move |&:|{i};
    }
    println!("{} {} {}", a[1](), a[5](), a[9]())
}

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