ORing Values in C++ With Vararg Template

orvalues.cpp

/*
One thing I like in like in languages like python and perl
is you can logically OR a series of values and it the 
expression will result in the first one that is 'non null'
or 'true'.   This facility is missing in C++  as the logical 
or operator(||) produces a boolean.

One thing to be cautious of, is that in python and perl
evalution of the OR'd expressions stops on the first one
that is true, any further expressions are not evalutated,
to include any potential side effects.

In the case of this implementation each parameter expression
is evaluated before the first invocation of OR_VALUES is made.

Typically this will not be an issue if you're using it to evaluate
pointers or references that have already been allocated/constructed,
However, if used with temporary objects whose construction takes place
as the parameter

Examples:
using std::string ;
string s = OR_VALUES(string("a"), string("b"), string("c")) ;

All three parameters will be constructed before OR_VALUES is invoked.

*/

/**
 * Terminal expansion of OR_VALUES
 * expanded when rest... only
 * unpacks one argument.
 */
template<typename Arg>
inline Arg OR_VALUES(const Arg& a)
{
    return a ;
}

/**
 * Expansion for any OR_VALUES having
 * two or more arguments
 */
template<typename Arg, typename ... Rest>
inline Arg OR_VALUES(const Arg& a, Rest... rest)
{
    if( a ) // consume Arg a
        return a ;
    return OR_VALUES(rest...) ;
}
#ifdef EXAMPLE
#include <iostream>

using namespace std ;

int main(int, char**)
{
  auto n1 = (const char*)nullptr ;
  auto n2 = (const char*)nullptr ;
  auto n3 = (const char*)nullptr ;
  auto foo = "foo" ;
  auto foo2 = "foo2" ;
  
  cout << OR_VALUES(foo) << endl ;
  cout << OR_VALUES(n1, foo) << endl ;
  cout << OR_VALUES(n1, n2, n3, foo) << endl ;
  cout << OR_VALUES(n1, n2, foo2, foo, n3) << endl ;
  return 0 ;
}
#endif