23 General utilities library [utilities]

Uses-allocator construction with allocator Alloc refers to the construction of an object obj of type T, using constructor arguments v1, v2, ..., vN of types V1, V2, ..., VN, respectively, and an allocator alloc of type Alloc, according to the following rules:

• (1.1)

  if uses_­allocator_­v<T, Alloc> is false and is_­constructible_­v<T, V1, V2, ..., VN> is true, then obj is initialized as obj(v1, v2, ..., vN);

• (1.2)

  otherwise, if uses_­allocator_­v<T, Alloc> is true and is_­constructible_­v<T, allocator_­arg_­t, Alloc, V1, V2, ..., VN> is true, then obj is initialized as obj(allocator_­arg, alloc, v1, v2, ..., vN);

• (1.3)

  otherwise, if uses_­allocator_­v<T, Alloc> is true and is_­constructible_­v<T, V1, V2, ..., VN, Alloc> is true, then obj is initialized as obj(v1, v2, ..., vN, alloc);

• (1.4)

  otherwise, the request for uses-allocator construction is ill-formed. [ Note: An error will result if uses_­allocator_­v<T, Alloc> is true but the specific constructor does not take an allocator. This definition prevents a silent failure to pass the allocator to an element.  — end note ]