std::allocator_arg, std::allocator_arg_t
From cppreference.com
| Defined in header <memory>
|
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| 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.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 |
See also
| (C++11) |
checks if the specified type supports uses-allocator construction (class template) |