闭合参数：传递一个突变内部变量的函数

发布于 2025-02-03 14:09:04 字数 1740 浏览 1 评论 0 原文

这个想法是要捕获状态（在这种情况下为 x ），将一个函数作为其参数（ alterer alterer <，在这种情况下为 canse_x ） /code>），这将决定内在状态如何变化。

pub fn plus17(h: & u64) -> u64 {
    *h + 17
}

pub fn main() {
    let x = 0; //take x by reference

    let mut change_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
    change_x(&mut plus17);

    println!("{}", x);
}

但是，我似乎不能正确地理解类型：

error[E0161]: cannot move a value of type dyn for<'r> FnOnce(&'r u64) -> u64: the size of dyn for<'r> FnOnce(&'r u64) -> u64 cannot be statically determined
  --> playground/src/main.rs:19:69
   |
19 |     let mut increment_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
   |                                                                     ^^^^^^^

error[E0507]: cannot move out of `*alterer` which is behind a shared reference
  --> playground/src/main.rs:19:69
   |
19 |     let mut increment_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
   |                                                                     ^^^^^^^ move occurs because `*alterer` has type `dyn for<'r> FnOnce(&'r u64) -> u64`, which does not implement the `Copy` trait

我不确定我是否有理由将 dyn 放在哪里，这是编译器的建议，我不确定为什么我为什么必须把它放在那里。是因为 Alterer 尽管输入/返回类型的＆amp; amp; u64-＆gt; u64 可能是任意大小的？

我还尝试使Alterer成为 fnmut ，而不是 fnonce ，但是我对它们的区别以及给定的更改> Alterer 只能运行一次（在外部闭合 change_x 的调用时）似乎是合理的。

原文

The idea is to to have one closure (change_x in this case) that captures state (x in this case) that takes a function as its parameter(alterer) that would dictate how the inner state changes.

pub fn plus17(h: & u64) -> u64 {
    *h + 17
}

pub fn main() {
    let x = 0; //take x by reference

    let mut change_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
    change_x(&mut plus17);

    println!("{}", x);
}

I can't seem to get the types right however:

error[E0161]: cannot move a value of type dyn for<'r> FnOnce(&'r u64) -> u64: the size of dyn for<'r> FnOnce(&'r u64) -> u64 cannot be statically determined
  --> playground/src/main.rs:19:69
   |
19 |     let mut increment_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
   |                                                                     ^^^^^^^

error[E0507]: cannot move out of `*alterer` which is behind a shared reference
  --> playground/src/main.rs:19:69
   |
19 |     let mut increment_x = move |alterer: &dyn FnOnce(&u64) ->u64 |  alterer(&x) ;
   |                                                                     ^^^^^^^ move occurs because `*alterer` has type `dyn for<'r> FnOnce(&'r u64) -> u64`, which does not implement the `Copy` trait

I'm not sure if i'm justified in putting the dyn where i put it, it was a compiler's suggestion and im not really sure why i have to put it there. Is it because the alterer can be of arbitrary size despite the input/return type of &u64->u64?

I have also tried to make alterer a FnMut as opposed to FnOnce, but im also pretty shaky as to their distinction and the fact that a given alterer would run only once (at the moment of invocation by outer closure change_x) seemed reasonable.