Operatorüberladung in C++ 

Ausdruck     als Elementfunktion  als freie Funktion
@a           (a).operator@()      operator@(a)   
a@b          (a).operator@(b)     operator@(a,b)          
a=b          (a).operator=(b) 
a[b]         (a).operator[](b) 
a->          (a).operator->() 
a@           (a).operator@(0)     operator@(a,0)

main.cpp

#include <initializer_list>
#include <ostream>
#include <iostream>
#include <vector>
using namespace ::std::literals;
template< class I >
static void print
( ::std::ostream & ostream, I const begin, I const top )
{ if( begin != top )
  { auto p = begin; 
    while( true )
    { ostream << *p++; 
      if( p == top )break;
      ostream << ", "s; }}}
template< class C >
static inline ::std::ostream & operator <<
( ::std::ostream & ostream, ::std::vector< C > const & vector )
{ ::print( ostream, cbegin( vector ), cend( vector )); 
  return ostream; }
int main()
{ ::std::vector< int >v = { 27, 28, 29 };
  ::std::cout << v << '\n'; }

transcript

27, 28, 29

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