Default function that just returns the passed value?

Question

As a lazy developer, I like to use this trick to specify a default function:

template 

        

Answer 1

boost::phoenix offers a complete functional toolbox, here 'arg1' is the ident to identity ;-)

#include 

template 
void index(X &x, Function f = Function()) {
    for (std::size_t i = 0; i < x.size(); ++i) {
            x[i] = f(i);
  }
}