std :: array的演绎指南 [英] deduction guides for std::array

问题描述

我遍历了C ++模板独特的书本，我试图了解 std :: array 的演绎指南是如何工作的.关于标准的定义，以下是声明

I go through the book C++ template unique quide and I try to understand how the deduction guides for std::array works. Regarding the definition of the standard the following is the declaration

template <class T, class... U>
array(T, U...) -> array<T, 1 + sizeof...(U)>;

例如，如果在主数组中创建为

For example if in main a array created as

std::array a{42,45,77} 

演绎如何发生?

谢谢

推荐答案

演绎如何发生?

很简单.

呼叫

std::array a{42,45,77}

匹配

array(T, U...)

具有 T = decltype(42)和 U ... = decltype(45)，decltype(77)即 T = int 和 U ... = int，int .

因此 a {42,45,47} 的类型变为 array< T，1 + sizeof ...(U)> ，因此std :: array< int，1 + sizeof ...(int，int)> ，因此 std :: array< int，1 + 2> 就是 std:: array< int，3>

So the type of a{42,45,47} become array<T, 1 + sizeof...(U)>, so std::array<int, 1 + sizeof...(int, int)>, so std::array<int, 1 + 2> that is std::array<int, 3>

换句话说:提取参数的类型；第一个( T )用于为类型指定数组(第一个模板参数)；其他仅用于计数( sizeof ...(U)).但是，对于模板的第二个参数，重要的是也要计算第一个参数(类型为 T 的值，因此 1 + sizeof ...(U中的 1 )).

In other words: are extracted the types of the arguments; the first one (T) is used to give the type the array (first template parameter); the others are used just to be counted (sizeof...(U)). But, for the template second parameter, it's important to count also the first argument (of type T, so the 1 in 1 + sizeof...(U)).

这篇关于std :: array的演绎指南的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！