std :: all_of不接受类成员函数作为具有1个参数的函数 [英] std::all_of not accepting class member function as function with 1 argument

问题描述

我无法弄清楚这次std::all_of通话中我在做什么.

I can't figure what I am doing wrong with this std::all_of call.

我上了一堂统计课:

class Statistics {
public:
bool isDataSet() const { return m_data.size() > 0; }
private:
std::vector<double> m_data;
};

Statistics类的每个实例都对应于某个对象.

Each instance of Statistics class corresponds to a certain object.

在另一个文件中的另一个函数中，我仅想在全部 Statistics实例中初始化数据后才显示统计信息.我想通过以下方式使用std::all_of函数:

In another function in a different file I want to display statistics only if data has been initialized in all Statistics instances. I want to use std::all_of function in the following manner:

if( std::all_of(m_stats.begin(), m_stats.end(), &Statistics::isDataSet) ) {
...
}

其中std::vector<Statistics*> m_stats.

编译器报告错误，因为谓词项的值不等于带有1个参数的函数".据我所知，每个类成员都将此指针作为第一个参数传递，因此Statistics::isDataSet()实际上应该是具有1个参数的函数.但是std::all_of认为这是错误的.

The compiler reports error in that the 'predicate term does not evaluate to a function taking 1 arguments'. As far as I know, each class member passes this pointer as the first parameter, so Statistics::isDataSet() should actually be a function with 1 parameter. But std::all_of sees this wrong.

我认为Statistics::isDataSet()应该作为std::all_of()中带有1个参数的函数接受吗?

Am I wrong in my assumption that Statistics::isDataSet() should be accepted as a function with 1 parameter in std::all_of()?

推荐答案

使用

std::bind(&Statistics::isDataSet, std::placeholders::_1)

或

[](const Statistics& s) { return s.isDataSet(); }

调用all_of时使用

代替&Statistics::isDataSet.后者期望一个 callable 类型(作为谓词)，并将一个Statistics实例传递给它.指定没有实例的成员函数显然不足以拨打电话

instead of &Statistics::isDataSet in call to all_of. latter expect a callable type (as predicate) and will pass an instance of Statistics to it. Specifying member-function w/o instance obviously not enough to make a call

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