Trait conflict between impl for T and something of FnMut() -> T

huangapple
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英文:

Trait conflict between impl for T and something of FnMut() -> T

问题

Here's the translated code you provided:

  1. pub trait ArrayFill<T, const LENGTH: usize>
  2. {
  3.     fn fill_into_array(self) -> [T; LENGTH];
  4. }
  6. impl<T, const LENGTH: usize> ArrayFill<T, LENGTH> for T
  7. where
  8.     T: Copy
  9. {
  10.     fn fill_into_array(self) -> [T; LENGTH]
  11.     {
  12.         [self; LENGTH]
  13.     }
  14. }
  15. impl<F, T, const LENGTH: usize> ArrayFill<T, LENGTH> for F
  16. where
  17.     F: FnMut() -> T
  18. {
  19.     fn fill_into_array(self) -> [T; LENGTH]
  20.     {
  21.         todo!()
  22.     }
  23. }

And the attempted solution code:

  1. #![feature(auto_traits)]
  2. #![feature(negative_impls)]
  4. auto trait NotFnMutToSelf {}
  5. impl<F> !NotFnMutToSelf for F
  6. where
  7.     F: FnMut() -> F {}
  9. pub trait ArrayFill<T, const LENGTH: usize>
  10. {
  11.     fn fill_into_array(self) -> [T; LENGTH];
  12. }
  14. impl<T, const LENGTH: usize> ArrayFill<T, LENGTH> for T
  15. where
  16.     T: Copy + NotFnMutToSelf
  17. {
  18.     fn fill_into_array(self) -> [T; LENGTH]
  19.     {
  20.         [self; LENGTH]
  21.     }
  22. }
  23. impl<F, T, const LENGTH: usize> ArrayFill<T, LENGTH> for F
  24. where
  25.     F: FnMut() -> T
  26. {
  27.     fn fill_into_array(self) -> [T; LENGTH]
  28.     {
  29.         todo!()
  30.     }
  31. }

I've provided the code translations as you requested. If you have any further questions or need assistance with specific parts of the code, please feel free to ask.

英文:

So i have this trait for filling an array from various types, however i get conflicting implementations for T and F: FnMut() -&gt; T. I'm guessing the only point of overlap would be the case of F: FnMut() -&gt; F, in which case the function F returns itself and equals T. Essentially, the compiler considers the possiblity of F being an FnMut() -&gt; (FnMut() -&gt; (FnMut() -&gt; ...)).

Here's the code, which will not compile:

  1. pub trait ArrayFill&lt;T, const LENGTH: usize&gt;
  2. {
  3.     fn fill_into_array(self) -&gt; [T; LENGTH];
  4. }
  6. impl&lt;T, const LENGTH: usize&gt; ArrayFill&lt;T, LENGTH&gt; for T
  7. where
  8.     T: Copy
  9. {
  10.     fn fill_into_array(self) -&gt; [T; LENGTH]
  11.     {
  12.         [self; LENGTH]
  13.     }
  14. }
  15. impl&lt;F, T, const LENGTH: usize&gt; ArrayFill&lt;T, LENGTH&gt; for F
  16. where
  17.     F: FnMut() -&gt; T
  18. {
  19.     fn fill_into_array(self) -&gt; [T; LENGTH]
  20.     {
  21.         todo!()
  22.     }
  23. }

I've tried using an auto-trait with a negative implementation for F: FnMut() -&gt; F, but even then conflict persists, as i don't think the compiler is able to reason properly with the negative implementation. The attempted solution is shown below:

  1. #![feature(auto_traits)]
  2. #![feature(negative_impls)]
  4. auto trait NotFnMutToSelf {}
  5. impl&lt;F&gt; !NotFnMutToSelf for F
  6. where
  7.     F: FnMut() -&gt; F {}
  9. pub trait ArrayFill&lt;T, const LENGTH: usize&gt;
  10. {
  11.     fn fill_into_array(self) -&gt; [T; LENGTH];
  12. }
  14. impl&lt;T, const LENGTH: usize&gt; ArrayFill&lt;T, LENGTH&gt; for T
  15. where
  16.     T: Copy + NotFnMutToSelf
  17. {
  18.     fn fill_into_array(self) -&gt; [T; LENGTH]
  19.     {
  20.         [self; LENGTH]
  21.     }
  22. }
  23. impl&lt;F, T, const LENGTH: usize&gt; ArrayFill&lt;T, LENGTH&gt; for F
  24. where
  25.     F: FnMut() -&gt; T
  26. {
  27.     fn fill_into_array(self) -&gt; [T; LENGTH]
  28.     {
  29.         todo!()
  30.     }
  31. }

I don't think specialization could solve it, because although the implementations overlap, neither of them overlap the other completely.

Any idea how to resolve this conflict?

答案1

得分: 2

很遗憾，这是不可能的。像这样的情况甚至在专业化RFC中被描述为提案RFC 不会 解决的问题。

英文:

Unfortunately, this is impossible. A situation like that was even described in the specialization RFC, as something the proposed RFC will not solve.

huangapple
  • 本文由 发表于 2023年7月3日 19:59:33
  • 转载请务必保留本文链接：https://go.coder-hub.com/76604530.html
  • rust
  • traits
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