std::allocator_arg, std::allocator_arg_t - cppreference.com (original) (raw)

Defined in header
struct allocator_arg_t { explicit allocator_arg_t() = default; }; (1) (since C++11)
constexpr std::allocator_arg_t allocator_arg {}; (2) (since C++11) (inline since C++17)

  1. std::allocator_arg_t is an empty class type used to disambiguate the overloads of constructors and member functions of allocator-aware objects, including std::tuple, std::function, std::packaged_task,(until C++17) and std::promise.

  2. std::allocator_arg is an instance of (1) that can be passed to the constructors and member functions of such permitted types.

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 2510 C++11 the default constructor was non-explicit, which could lead to ambiguity made explicit

[edit] See also

| | checks if the specified type supports uses-allocator construction (class template) [edit] | | ---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- |