/* File: lambda4.cpp
   
   An example of a lambda expression capturing
   a global variable count.

   This program compiles with GNU g++ with a warning, 
   but not with clang g++ (as of Oct 13, 2021).

   In GNU g++, calling the returned lambda expression
   changes the value of the global, even though
   count is captured by value.

*/

#include <iostream>

// must #include <functional> to use std::function< >
//
#include <functional>

using namespace std ;

int count=0 ;

std::function< int(int) > makeAddXLambda(int x) {
   return [x,count](int n){ return n+x+(count++) ; } ;
}


int main () {

   std::function< int(int) > add3 = makeAddXLambda(3) ;
   cout << "add3(5) = " << add3(5) << endl ;
   cout << "count = " << count << endl ;
   cout << "add3(5) = " << add3(5) << endl ;
   cout << "count = " << count << endl ;
   cout << "add3(5) = " << add3(5) << endl ;
   cout << "count = " << count << endl ;


   std::function< int(int) > add5 = makeAddXLambda(5) ;
   cout << "add5(8) = " << add5(8) << endl ;
   cout << "count = " << count << endl ;
   cout << "add5(8) = " << add5(8) << endl ;
   cout << "count = " << count << endl ;
   cout << "add5(8) = " << add5(8) << endl ;
   cout << "count = " << count << endl ;

}