std::piecewise_construct_t
STD：分段[医]构造[医]T型
| Defined in header | | |
|---|---|---|
| struct piecewise_construct_t { }; | | (since C++11) (until C++17) |
| struct piecewise_construct_t { explicit piecewise_construct_t() = default; }; | | (since C++17) |
std::piecewise_construct_t是一个空的struct标记类型，用于消除使用两个元组参数的不同函数之间的歧义。
不使用的重载std::piecewise_construct_t假设每个元组参数都成为一对的元素。使用的过载std::piecewise_construct_t假设每个元组参数都用于构造一个指定类型的新对象，该对象将成为该对的元素。
例
二次
#include <iostream>
#include <utility>
#include <tuple>
struct Foo {
Foo(std::tuple<int, float>)
{
std::cout << "Constructed a Foo from a tuple\n";
}
Foo(int, float)
{
std::cout << "Constructed a Foo from an int and a float\n";
}
};
int main()
{
std::tuple<int, float> t(1, 3.14
std::pair<Foo, Foo> p1(t, t
std::pair<Foo, Foo> p2(std::piecewise_construct, t, t
}
二次
产出：
二次
Constructed a Foo from a tuple
Constructed a Foo from a tuple
Constructed a Foo from an int and a float
Constructed a Foo from an int and a float
二次
另见
| piecewise_construct (C++11) | an object of type piecewise_construct_t used to disambiguate functions for piecewise construction (constant) |
|---|---|
| (constructor) | constructs new pair (public member function of std::pair) |
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