迭代一系列泛型类型 [英] Iterating over a range of generic type

问题描述

我有特质

 特质B {
类型索引：大小+复制; 
 fn bounds（& self） - > （自我::索引，自我::索引）; 
} 
  

我想获得所有指数 es bounds ：

  fn iterate< T： B>（它：& T）{
 let（low，high）= it.bounds（）; 
 for i in low..high {} 
} 
  

这赢得了'因为没有约束类型 T 可以远程结束，并且编译器说了这么多：

< pre class =lang-none prettyprint-override> 错误[E0277]：特征绑定`< T as B> :: Index：std :: iter :: Step`不满足
- > src / main.rs:8：5
|
8 |因为我在低..高{}
| ^^^^^^^^^^^^^^^^^^^^^特征`std :: iter :: Step`未实现`< T as B> :: Index`
|
= help：考虑添加一个`where< T as B> :: Index：std :: iter :: Step` bound
= note：required因为对std的impl的要求： ：iter :: Iterator` for`std :: ops :: Range<< T as B> :: Index>`


我尝试添加步骤绑定到索引

 使用std :: iter :: Step; 
 
特质B {
类型索引：大小+复制+步骤; 
 fn bounds（& self） - > （自我::索引，自我::索引）; 
} 
  

但显然不稳定：

 错误：使用不稳定的库特征'step_trait'：可能被更细粒度的特征所取代（参见问题＃42168）
  - > src / main.rs:1：5 
 | 
 1 |使用std :: iter :: Step; 
 | ^^^^^^^^^^^^^^^ 
 
错误：使用不稳定的库特征'step_trait'：可能被更细粒度的特征所取代（参见问题＃42168）
  - > src / main.rs:4:32 
 | 
 4 |类型索引：大小+复制+步骤; 
 | ^^^^ 
  

我错过了什么或者现在是不可能这样做的？

解决方案

如果你想要一个范围< T> 可以迭代过来，只需使用它作为你的特征界限：

  trait有界{
类型索引：大小+复制; 
 fn bounds（& self） - > （自我::索引，自我::索引）; 
} 
 
 fn iterate< T>（it：& T）
其中
 T：Bounded，
 std :: ops :: Range< T :: Index>：IntoIterator，
 {
 let（low，high）= it.bounds（）; 
 for i in low..high {} 
} 
 
 fn main（）{} 
  

I have a trait

trait B {
    type Index: Sized + Copy;
    fn bounds(&self) -> (Self::Index, Self::Index);
}

I want to get all the Indexes within bounds:

fn iterate<T: B>(it: &T) {
    let (low, high) = it.bounds();
    for i in low..high {}
}

This won't work since there's no constraint that the type T can be "ranged" over, and the compiler says as much:

error[E0277]: the trait bound `<T as B>::Index: std::iter::Step` is not satisfied
 --> src/main.rs:8:5
  |
8 |     for i in low..high {}
  |     ^^^^^^^^^^^^^^^^^^^^^ the trait `std::iter::Step` is not implemented for `<T as B>::Index`
  |
  = help: consider adding a `where <T as B>::Index: std::iter::Step` bound
  = note: required because of the requirements on the impl of `std::iter::Iterator` for `std::ops::Range<<T as B>::Index>`

I tried adding the Step bound to Index

use std::iter::Step;

trait B {
    type Index: Sized + Copy + Step;
    fn bounds(&self) -> (Self::Index, Self::Index);
}

but apparently it isn't stable:

error: use of unstable library feature 'step_trait': likely to be replaced by finer-grained traits (see issue #42168)
 --> src/main.rs:1:5
  |
1 | use std::iter::Step;
  |     ^^^^^^^^^^^^^^^

error: use of unstable library feature 'step_trait': likely to be replaced by finer-grained traits (see issue #42168)
 --> src/main.rs:4:32
  |
4 |     type Index: Sized + Copy + Step;
  |                                ^^^^

Am I missing something or is it just not possible to do so right now?

解决方案

If you want to require that a Range<T> can be iterated over, just use that as your trait bound:

trait Bounded {
    type Index: Sized + Copy;
    fn bounds(&self) -> (Self::Index, Self::Index);
}

fn iterate<T>(it: &T)
where
    T: Bounded,
    std::ops::Range<T::Index>: IntoIterator,
{
    let (low, high) = it.bounds();
    for i in low..high {}
}

fn main() {}

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