在类上启用std :: get支持

本文介绍了在类上启用std :: get支持的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！ 问题描述

我要专门支持std :: get的模板是什么？

What are the templates that I have to specialize to support std::get?

struct MyClass { int a; }; template <const size_t I> struct MyContainer { MyClass array[I]; };

我必须专门做什么才能做到：

What do I have to specialize to be able to do:

MyContainer<16> mc; std::get<0>(mc);

推荐答案

std :: get 不是标准库的自定义点;三个函数模板重载（ pair ， tuple 和数组）不明确允许用户定义的重载，因此17.6.4.2.1p1适用并添加一个自己的函数模板重载的声明是未定义的行为。

std::get is not a customization point for the standard library; the three function template overloads (for pair, tuple and array) do not explicitly allow for user-defined overloads, so 17.6.4.2.1p1 applies and adding a declaration of your own function template overload is undefined behaviour.

，如果您 写：

namespace std { template<size_t I, size_t N> MyClass &get(MyContainer<N> &c) { return c.array[I]; } }

同样，对于右值引用和const引用重载，

and similarly for the rvalue reference and const reference overloads, your program would likely work as you expect.

但是，很少有人认为标准已经提供数组：

However, there's little point seeing as the standard already supplies array:

template<size_t N> using MyContainer = std::array<MyClass, N>;