Feature request: Singleton allocators #294
Description
If each static variable storing an allocator were wrapped in the Default method of a different named ZST, then through an extension trait it would be possible to use methods like Box::from and Iterator::<Vec<_>::collect() with the same syntax as with the global allocator. That would be handy because it'd mean not having to change any code except for defining the ZST, creating/destroying the instance, and adding it to function and type signatures. Could we please have an interface of that kind so that porting away from the global allocator would be easier?