std::allocator_arg, std::allocator_arg_t
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Defined in header
<memory>
struct allocator_arg_t { explicit allocator_arg_t() = default; };
(1)
(since C++11)
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 |