Defined in header <memory> | ||
|---|---|---|
struct allocator_arg_t { explicit allocator_arg_t() = default; };
| (since C++11) | |
constexpr std::allocator_arg_t allocator_arg = std::allocator_arg_t(); | (since C++11) (until C++17) | |
inline constexpr std::allocator_arg_t allocator_arg = std::allocator_arg_t(); | (since C++17) |
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. std::allocator_arg is a constant of it.
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 |
|
(C++11) | checks if the specified type supports uses-allocator construction (class template) |
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