使用花括号来初始化元组的std ::数组 [英] Initialize an std::array of tuples with curly braces

问题描述

这可能有一个非常简单的答案，但我真的不能弄清楚。为什么我会收到错误这样做？

This probably has a very simple answer, but I really can't figure it out. Why do I get errors for doing this? What's the correct way to initialize something like this?

std::array<std::tuple<int, std::string>, 3> tuples{
    {3, "a"},
    {7, "b"},
    {2, "c"}
};

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在MSVC 2015上，我遇到以下错误：

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On MSVC 2015, I get the following errors:

No suitable constructor exists to convert from "int" to "std::tuple<int, std::string>"
No suitable constructor exists to convert from "const char[2]" to "std::tuple<int, std::string>"

推荐答案

> tuple 。请参阅其在C ++ 11/14中的构造函数 explicit 。因此，它不能参与拷贝列表初始化，这是内部支撑初始化列表做的（外部的是直接列表初始化）。

This is an outstanding issue with tuple. See, its constructor in C++11/14 is explicit. And therefore, it cannot participate in copy-list-initialization, which is what the inner braced-init-lists do (the outer ones are direct-list-initialization).

这个想法是阻止你绕过类的显式构造函数通过 tuple 。但是，在C ++ 17中，这将改变：如果所有的元组类型本身都是可以从相应的给定类型隐式转换的，那么 tuple 。

The idea was to prevent you from being able to bypass a class's explicit constructors through tuple. But, in C++17, this will be changed: if all of the tuple's types themselves are implicitly convertible from the respective given type, then so too will that constructor of tuple.

对于特定的用例，可以使用std :: pair。它的构造函数从不显式。

For your specific use case, you could use std::pair. Its constructor is never explicit.

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