C++ lambda expression

emerged since c++11, lambda expression/function is an unnamed function object capable of capturing variables in scope.

1. syntax of a lambda expression

[ captures ] <tparams>(optional)(c++20) ( params ) specifiers exception attr -> ret requires(optional)(c++20){ body }

[ captures ] ( params ) -> ret { body }

[ captures ] ( params ) { body }

[ captures ] { body } 

examples:

 [](){}   //barebone lambda

 [](){}() // immediately execute a lambda

auto print = [](const int& n) { n = n+1; std::cout << " " << n; };

std::for_each(v.begin(), v.end(), print); // caller of the lambda expression

std::for_each(v.begin(), v.end(), [](int &n){ n++; });