template <class T, class Alloc> struct uses_allocator;
Remarks: Automatically detects whether T has a nested allocator_type that is convertible from Alloc. Meets the BinaryTypeTrait requirements. The implementation shall provide a definition that is derived from true_type if the qualified-id T::allocator_type is valid and denotes a type ([temp.deduct]) and is_convertible_v<Alloc, T::allocator_type> != false, otherwise it shall be derived from false_type. A program may specialize this template to derive from true_type for a user-defined type T that does not have a nested allocator_type but nonetheless can be constructed with an allocator where either:
the first argument of a constructor has type allocator_arg_t and the second argument has type Alloc or
the last argument of a constructor has type Alloc.