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Showing content from https://cplusplus.com/function::target_type below:

public member function

<functional>

const type_info& target_type() const noexcept;

Target type_info

The function returns the same as applying the typeid operator to the type of the callable object used as target.

If the object has no target (i.e., it is an empty function), this function returns typeid(void).

Note that a single type instantiation of function is able to hold different target types with the same calling signatures: for example, the same function object may hold a pointer to a function or a function object.

type_info is a type defined in header <typeinfo> that can be used to compare types.

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// function::target_type example
#include <iostream>     // std::cout, std::boolalpha
#include <functional>   // std::function, std::plus, std::minus
#include <typeinfo>     // typeid

int  plus_function(int a, int b) {return a+b;}
int minus_function(int a, int b) {return a-b;}

int main () {
  std::function<int(int,int)> plus1  = plus_function;
  std::function<int(int,int)> plus2  = std::plus<int>();
  std::function<int(int,int)> minus1 = minus_function;
  std::function<int(int,int)> minus2 = std::minus<int>();

  std::cout << "pointers as targets:\n" << std::boolalpha;
  std::cout << "plus1 : " << ( plus1.target_type()==typeid(int(*)(int,int))) << '\n';
  std::cout << "plus2 : " << ( plus2.target_type()==typeid(int(*)(int,int))) << '\n';
  std::cout << "minus1: " << (minus1.target_type()==typeid(int(*)(int,int))) << '\n';
  std::cout << "minus2: " << (minus2.target_type()==typeid(int(*)(int,int))) << '\n';
  std::cout << '\n';

  std::cout << "same type?:\n";
  std::cout << "(plus1, plus2) : " << ( plus1.target_type()== plus2.target_type()) << '\n';
  std::cout << "(minus1,minus2): " << (minus1.target_type()==minus2.target_type()) << '\n';
  std::cout << "(plus1, minus1): " << ( plus1.target_type()==minus1.target_type()) << '\n';
  std::cout << "(plus2, minus2): " << ( plus2.target_type()==minus2.target_type()) << '\n';

  return 0;
}

pointers as targets:
plus1 : true
plus2 : false
minus1: true
minus2: false

same type?:
(plus1, plus2) : false
(minus1,minus2): false
(plus1, minus1): true
(plus2, minus2): false

function::target

Get pointer to target (public member function)

function::operator bool

Check if callable (public member function)

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