函子结构的 C++ 类型

Question

I am trying to have a single variable with some type that can be assigned to some of the C++ standard functors (eg: std::plus , std::multiplies , etc...)

Here is the definition for std::plus (from this link ):

template <class T> struct plus : binary_function <T,T,T> {
  T operator() (const T& x, const T& y) const {return x+y;}
};

I tried

#include <functional>

std::binary_function<int, int, int> func = std::plus;

but it doesn't work. How do I define it properly?

Answer 1

A single variable to hold all kinds of callables with same signature is std::function<int(int,int)> . Though the functors need to either have the template argument specified or deducde them from arguments:

std::function<int(int,int)> func2 = [](int a,int b){ return std::plus{}(a,b);};

or

std::function<int(int,int)> func = std::plus<int>{};