Suggestion: allow the constructors without `_in` for allocator types that implement `Default`

[Rua]

In my case, the allocator is just an empty struct that calls global functions, but it's not the global allocator. Having to pass Default::default() to every constructor is awkward. Is it possible to make the standard constructors like new, new_uninit etc available to non-standard allocators if the allocator implements Default? Then I can just do this:

type MyBox<T> = Box<T, MyAllocator>;
MyBox::new(foo)

[Amanieu]

Unfortunately we can't make this change because it would break type inference for a huge portion of the ecosystem. This is the same reason why HashMap::new only works with the default hasher, even if you are using a custom hasher that implements Default.

[CAD97]

Highly relevant: Gankra's article Defaults Affect Inference in Rust: Expressions Instead Of Types