C++ type for functor structs

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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?

c++14 c++17 functor c++11 c++
1 Answers

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>{};
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