std::pmr::polymorphic_allocator::construct
STD：：PMR：：多态[医]分配程序：：构造
| template < class U, class... Args > void construct( U* p, Args&&... args | (1) | (since C++17) |
|---|---|---|
| template< class T1, class T2, class... Args1, class... Args2 > void construct( std::pair<T1, T2>* p, std::piecewise_construct_t, std::tuple<Args1...> x, std::tuple<Args2...> y | (2) | (since C++17) |
| template< class T1, class T2 > void construct( std::pair<T1, T2>* p | (3) | (since C++17) |
| template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, U&& x, V&& y | (4) | (since C++17) |
| template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, const std::pair<U, V>& xy | (5) | (since C++17) |
| template< class T1, class T2, class U, class V > void construct( std::pair<T1, T2>* p, std::pair<U, V>&& xy | (6) | (since C++17) |
pthis->resource()
1%29std::uses_allocator<U, memory_resource*>::value==false28%Ustd::is_constructible<U, Args...>::value==true，然后将对象构造为::new((void*) p) U(std::forward<Args>(args)... ...
否则，如果std::uses_allocator<U, memory_resource*>::value==true28%U使用分配器，例如它是一个容器%29和std::is_constructible<U,std::allocator_arg_t, memory_resource*, Args...>::value==true，然后将对象构造为::new((void*) p) U(std::allocator_arg, this->resource(),std::forward<Args>(args)... ...
否则，如果std::uses_allocator<U, memory_resource*>::value==true28%U使用分配器，例如它是一个容器%29和std::is_constructible<U, Args..., memory_resource*>::value==true，然后将对象构造为::new((void*) p) U(std::forward<Args>(args)..., this->resource()...
否则，这个程序就会有错误的形式。
T1或T2是分配器感知的，可以修改元组。x和y包括this->resource()，产生了两个新的元组。xprime和yprime根据以下三条规则：
2A%29T1不知道分配器的百分比28std::uses_allocator<T1, memory_resource*>::value==false29%和std::is_constructible<T1, Args1...>::value==true，然后xprime是x，未经修饰。
2B%29T1是否分配器感知%28std::uses_allocator<T1, memory_resource*>::value==true%29，其构造函数接受分配器标记%28std::is_constructible<T1,std::allocator_arg_t, memory_resource*, Args1...>::value==true，然后xprime是std::tuple_cat(std::make_tuple(std::allocator_arg, this->resource()), std::move(x))...
2C%29T1是否分配器感知%28std::uses_allocator<T1, memory_resource*>::value==true%29，其构造函数将分配程序作为最后一个参数%28。std::is_constructible<T1, Args1..., memory_resource*>::value==true%29，那么xprime是std::tuple_cat(std::move(x),std::make_tuple(this->resource()))...
2D%29，否则，程序是错误的.
同样的规则适用于T2和替换y带着yprime...
一次xprime和yprime构造，构造成对p在分配的存储中，就好像::new((void*) p) pair<T1, T2>(std::piecewise_construct, std::move(xprime), std::move(yprime)
3%29相当于construct(p,std::piecewise_construct,std::tuple<>(),std::tuple<>())也就是说，如果接受的话，将内存资源传递给对%27s成员类型。
4%29相当于。
construct(p,std::piecewise_construct,std::forward_as_tuple(std::forward<U>(x)),
std::forward_as_tuple(std::forward<V>(y)))...
5%29相当于。
construct(p,std::piecewise_construct,std::forward_as_tuple(xy.first),
std::forward_as_tuple(xy.second))...
6%29相当于。
construct(p,std::piecewise_construct,std::forward_as_tuple(std::forward<U>(xy.first)),
std::forward_as_tuple(std::forward<V>(xy.second)))...
参数
| p | - | pointer to allocated, but not initialized storage |
|---|---|---|
| args... | - | the constructor arguments to pass to the constructor of T |
| x | - | the constructor arguments to pass to the constructor of T1 |
| y | - | the constructor arguments to pass to the constructor of T2 |
| xy | - | the pair whose two members are the constructor arguments for T1 and T2 |
返回值
%280%29
注记
这个函数被称为%28std::allocator_traits%29由任何分配器感知对象执行，如std::pmr::vector%28或其他std::vector给了我一个std::std::polymorphic_allocator作为分配程序使用%29。自memory_resource*隐式转换为polymorphic_allocator，内存资源指针将使用多态分配器传播到任何感知分配器的子对象。
另见
| construct static | constructs an object in the allocated storage (function template) |
|---|---|
| construct (deprecated in C++17) | constructs an object in allocated storage (public member function of std::allocator) |
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