[英]How can I abstract Realm notifications into a generic struct with a closure?
[英]How can I store a closure object in a struct?
我不知道如何將閉包 object 存儲在結構中。 arguments 和返回用於閉合 object 是已知的。 這是我的精簡代碼:
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", op: |a,b| a },
// Instr { name: "qwer", op: |a,b| a }
// ];
}
坦率地說,我不明白這些錯誤是什么意思。 在我看來,這很簡單。 閉包具有類型和已知尺寸。 將其存儲在相同類型的類型字段中應該很簡單。 正確的?
嘗試添加F: ?Sized
作為錯誤消息提示的並不能修復“編譯時未知大小”錯誤。
有人可以幫我正確編譯嗎?
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],[i32;3]) -> [i32;4]> = Instr { name: "asd".to_string(), op: |a,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],[i32;3]) -> [i32;4]> = Instr { name: "asd".to_string(), op: |a,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],[i32;3]) -> [i32;4]> = Instr { name: "asd".to_string(), op: |a,b| a};
| ^^^^^^^ expected trait object `dyn Fn`, found closure
|
= note: expected trait object `dyn Fn([i32; 4], [i32; 3]) -> [i32; 4]`
found closure `[closure@a.rs:11:92: 11:99]`
不同的閉包具有不同的大小,因此您不能在結構中存儲“原始閉包”或“原始特征對象”,它們必須位於指針后面,因此您可以將它們放在Box
中,如下所示:
struct Instr {
name: String,
op: Box<dyn Fn([i32; 4], [i32; 3]) -> [i32; 4]>,
}
fn main() {
let instrs = vec![
Instr { name: "asdf".into(), op: Box::new(|a,b| a) },
Instr { name: "qwer".into(), op: Box::new(|a,b| a) }
];
}
接受的答案完美地解決了您的用例的解決方案,但我想澄清“未調整大小”的錯誤消息以及“簡單示例”無法正常工作。
Rust 完全能夠按照問題中的定義將閉包存儲在Instr
中,但是您的類型規范將其混淆了。 每個閉包的類型都是匿名的,你不能命名它。 您嘗試通過拼寫特征Fn(ARGS...) -> RESULT
來指定閉包類型是錯誤的,因為在 Rust 中,當您使用預期類型的特征時,它指的是特征的動態實現,又名特征 object 。 特征 object 沒有大小,必須通過引用或智能指針訪問。
因此,如果您讓 Rust 推斷其類型,您可以創建一個帶有任意閉包的Instr
:
struct Instr<F>
where F: Fn([i32;4],[i32;3]) -> [i32;4]
{
name: String,
op: F
}
fn main()
{
// Simple example
let tmp : Instr<_> = Instr { name: "asd".to_string(), op: |a,b| a};
}
但這不允許您創建一個Instr
的向量,每個向量都有不同的閉包,因為這些Instr
將具有不同的類型。 為此,您需要使用參考或Box
,如接受的答案所示。
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