// Illustration of mutable in context of lambda expressions.

#include <iostream>     
#include <string>

int main () {
  int p{7};

  auto f7 = [p](){++p;};                        // COMPILE TIME ERROR: increment of read-only variable p
  auto f8 = [p]()mutable{++p;};                 // now OK, but strange.  Does NOT affect p in main
  auto f9 = [&p](){++p;};                       // OK: Does affects p in main.

  f8();                                         // A local copy of p is incremented. p in pmain unaffected.
  std::cout << "p: " << p << std::endl;         // p: 7

  f9();                                         // p in main is incremented, via the reference.
  std::cout << "p: " << p << std::endl;         // p: 8
}