如何在结构中存储闭包对象？

问题描述

我不知道如何在结构中存储闭包对象。闭包对象的参数和返回值是已知的。这是我的精简代码：

struct Instr<F>
    where F: Fn([i32;4],[i32;3]) -> [i32;4]
{
    name: String,op: F
}

fn main()
{
    // Simple example showing the difficulty:
    let tmp : Instr<Fn([i32;4],[i32;3]) -> [i32;4]> = Instr { name: "asd".to_string(),op: |a,b| a};

    // What I really want is something more like this:
    // let instrs = vec![
    //     Instr { name: "asdf",b| a },//     Instr { name: "qwer",b| a }
    // ];
}

坦率地说，我不明白这些错误是什么意思。在我看来，这很简单。封闭件具有类型和已知尺寸。将它存储在相同类型的类型字段中应该很简单。对吗？

按照错误消息的提示尝试添加 F: ?Sized 并不能解决“编译时大小未知”错误。

有人能帮我正确编译吗？

error[E0277]: the size for values of type `dyn Fn([i32; 4],[i32; 3]) -> [i32; 4]` cannot be known at compilation time
  --> a.rs:11:15
   |
1  | struct Instr<F>
   |              - required by this bound in `Instr`
...
11 |     let tmp : Instr<Fn([i32;4],b| a};
   |               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn Fn([i32; 4],[i32; 3]) -> [i32; 4]`
help: you could relax the implicit `Sized` bound on `F` if it were used through indirection like `&F` or `Box<F>`
  --> a.rs:1:14
   |
1  | struct Instr<F>
   |              ^ this could be changed to `F: ?Sized`...
2  |     where F : Fn([i32;4],[i32;3]) -> [i32;4]
   |           - ...if indirection was used here: `Box<F>`
...
5  |     op : F
   |          - ...if indirection was used here: `Box<F>`

error[E0277]: the size for values of type `dyn Fn([i32; 4],[i32; 3]) -> [i32; 4]` cannot be known at compilation time
  --> a.rs:11:55
   |
1  | / struct Instr<F>
2  | |     where F : Fn([i32;4],[i32;3]) -> [i32;4]
3  | | {
4  | |     name : String,5  | |     op : F
6  | | }
   | |_- required by `Instr`
...
11 |       let tmp : Instr<Fn([i32;4],b| a};
   |                                                         ^^^^^ doesn't have a size known at compile-time
   |
   = help: the trait `Sized` is not implemented for `dyn Fn([i32; 4],[i32; 3]) -> [i32; 4]`

error[E0308]: mismatched types
  --> a.rs:11:92
   |
11 |     let tmp : Instr<Fn([i32;4],b| a};
   |                                                                                            ^^^^^^^ expected trait object `dyn Fn`,found closure
   |
   = note: expected trait object `dyn Fn([i32; 4],[i32; 3]) -> [i32; 4]`
                   found closure `[[email protected]:11:92: 11:99]`

解决方法

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closures generics trait-objects