如何在初始化列表中使用std :: map :: operator = [英] How to use std::map::operator= with initializer lists

问题描述

我在> 前问过有关(没有得到回答)，然后我想也许使用括号初始化会有所帮助，但没有帮助.

I asked the same question before about boost::assign::map_list_of (which didn't get answered), then I thought maybe using brace initialization would help, but it didn't.

这很完美:

std::map<int, char> m = {{1, 'a'}, {3, 'b'}, {5, 'c'}, {7, 'd'}};

但这不是:

std::map<int, char> m;
m = {{1, 'a'}, {3, 'b'}, {5, 'c'}, {7, 'd'}};

Visual Studio 2013给出错误error C2593: 'operator =' is ambiguous，可能是operator=(std::initalizer_list)或operator=(std::map&&).

Visual Studio 2013 gives the error error C2593: 'operator =' is ambiguous, could be either operator=(std::initalizer_list) or operator=(std::map&&).

是否可以使用第二个版本?例如，对于m是成员变量的情况.

Is it possible to get the second version to work? For cases where m is a member variable, for example.

推荐答案

您可以构造一个临时文件并将其用于作业.

You could construct a temporary and use it in the assignment.

std::map<int, char> m;
m = std::map<int, char>{{1, 'a'}, {3, 'b'}, {5, 'c'}, {7, 'd'}};

如果不想重复输入，可以使用decltype.

If you don't want to repeat the type, you can use decltype.

std::map<int, char> m;
m = decltype(m){{1, 'a'}, {3, 'b'}, {5, 'c'}, {7, 'd'}};

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