存储lambda函数，将作用域变量作为类成员进行重用 [英] Store lambda function that captures the scope variable as a class member to reuse

问题描述

在我的类很多方法有这样的代码片段：

In my class lots of methods have such a snippet:

std::string str = getSomeStr();

auto it = std::find_if(
vec.begin(), 
vec.end(), 
[str](const std::string& b){return str + "abc" == b;});

因此，我想存储lambda函数来重用它。但它从范围捕获 str 。

Therefore, I want to store the lambda function to reuse it. But it captures the str from the scope. How I should do that?

推荐答案

如果我理解它的话...

If I understood it right...

class MyOperation {
    std::string s;
public:
    MyOperation(std::string s) : s(s) { }

    operator()(const std::string& b) {
        return s + "abc" == b;
    }
};

用法：

std::string str = getSomeStr();

auto it = std::find_if(
    vec.begin(), 
    vec.end(), 
    MyOperation(str));

您不必使用 str temporary，或者使 MyOperation 只保存一个 std :: string 引用。

You don't have to use the str temporary, or make MyOperation hold only a std::string reference. This depends on what do you want to achieve.

当然，你可以这么做：

auto myOperation(std::string s) { 
    return [&s](const std::string& b) {
        return s + "abc" == b;
    };
}

但我没有看到这一点，坦率地说。

But I don't see the point, frankly.

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