libstd: Use std::array::from_fn to implement Default for arrays larger than 32 elements. #124163
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cc some of the people involved in #74060: @withoutboats @nikomatsakis @SimonSapin |
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…r than 32 elements. Much like rust-lang#74060 did for every other trait. This avoids tools like rust-bindgen having to painfully work around this limitations, sometimes incorrectly like in rust-lang/rust-bindgen#2803
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| fn default() -> [T; $n] { [] } | ||
| } | ||
| }; | ||
| #[stable(feature = "default_array_lib", since = "1.79.0")] |
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I don't know if this is the right thing to do annotation wise.
| // The Default impls cannot be done with const generics because `[T; 0]` doesn't | ||
| // require Default to be implemented, and having different impl blocks for | ||
| // different numbers isn't supported yet. |
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Oh... I totally misread that, ugh
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So I could fix this by using a conditional impl using generic_const_exprs, but that causes a bunch of other code in libcore to fail to build, see #124167
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Is there any other clever way of getting this to work out of curiosity? (Not familiar with the specialisation features that are available in nightly)
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generic_const_exprs is very much forbidden from being used on the standard library, no matter this issue. it's way too broken for that.
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Closing for the reason stated. There is no way that this can currently be done in the standard library, as the necessary features are simply not mature enough. Personally, the last time I tried to implement |
Much like #74060 did for every other trait.
This avoids tools like rust-bindgen having to painfully work around this limitations, sometimes incorrectly like in
rust-lang/rust-bindgen#2803