如何使用閉包而不是特質？

Question

我想註冊Gen::my_g作爲回調。簡單的方法是實現trait Foo爲Gen，但我不想爲Gen實施trait Foo。

換句話說，我想註釋掉標記爲B!!!的代碼並取消註釋標記爲A!!!的代碼。

這不是我的代碼;我不能修改這個：

struct S1; 

struct TT; 
trait MyRes {} 

trait Foo { 
    fn g<'a>(&self, ecx: &'a mut S1, tt: &[TT]) -> Box<MyRes + 'a>; 
} 

impl<F> Foo for F 
where 
    F: for<'a> Fn(&'a mut S1, &[TT]) -> Box<MyRes + 'a>, 
{ 
    fn g<'a>(&self, ecx: &'a mut S1, tt: &[TT]) -> Box<MyRes + 'a> { 
     (*self)(ecx, tt) 
    } 
} 

fn f1<F>(name: &str, extension: F) 
where 
    F: Foo + 'static, 
{ 
} 

這是我的代碼：

struct Gen {} 
impl Gen { 
    fn register(self) { 

     //  f1("aaa", move |ecx, tt| self.my_g(ecx, tt));//A!!! 

     f1("aaa", self); //B!!! 
    } 

    fn my_g<'a>(&self, ecx: &'a mut S1, tt: &[TT]) -> Box<MyRes + 'a> { 
     unimplemented!(); 
    } 
} 

impl Foo for Gen { 
    fn g<'a>(&self, ecx: &'a mut S1, tt: &[TT]) -> Box<MyRes + 'a> { 
     self.my_g(ecx, tt) 
    } 
} 

如果我取消//A!!!，編譯器會告訴我的東西，我不明白：

error[E0271]: type mismatch resolving `for<'a, 'r> <[closure@src/main.rs:29:19: 29:52 self:_] as std::ops::FnOnce<(&'a mut S1, &'r [TT])>>::Output == std::boxed::Box<MyRes + 'a>` 
    --> src/main.rs:29:9 
    | 
29 |   f1("aaa", move |ecx, tt| self.my_g(ecx, tt)); //A!!! 
    |   ^^ expected bound lifetime parameter, found concrete lifetime 
    | 
    = note: concrete lifetime that was found is lifetime '_#12r 
    = note: required because of the requirements on the impl of `Foo` for `[closure@src/main.rs:29:19: 29:52 self:_]` 
    = note: required by `f1` 

error[E0281]: type mismatch: `[closure@src/main.rs:29:19: 29:52 self:_]` implements the trait `std::ops::Fn<(&mut S1, &[TT])>`, but the trait `for<'a, 'r> std::ops::Fn<(&'a mut S1, &'r [TT])>` is required 
    --> src/main.rs:29:9 
    | 
29 |   f1("aaa", move |ecx, tt| self.my_g(ecx, tt)); //A!!! 
    |   ^^  --------------------------------- implements `std::ops::Fn<(&mut S1, &[TT])>` 
    |   | 
    |   requires `for<'a, 'r> std::ops::Fn<(&'a mut S1, &'r [TT])>` 
    |   expected concrete lifetime, found bound lifetime parameter 
    | 
    = note: required because of the requirements on the impl of `Foo` for `[closure@src/main.rs:29:19: 29:52 self:_]` 
    = note: required by `f1` 

Answer 1

這是已知問題：

• Confusing type error due to strange inferred type for a closure argument

鏽病編譯器目前不能推斷出的封閉是有效的任何壽命（這是什麼的Foo::g的類型要求）。它會推斷任何具體的壽命，但不會超出這個範圍。