I have designed a parameter class which allows me to write code like this:
//define parameter
typedef basic_config_param<std::string> name;
void test(config_param param) {
if(param.has<name>()) { //by name
cout << "Your name is: " << param.get<name>() << endl;
}
unsigned long & n = param<ref<unsigned long> >(); //by type
if(param.get<value<bool> >(true)) { //return true if not found
++n;
}
}
unsigned long num = 0;
test(( name("Special :-)"), ref<unsigned long>(num) )); //easy to add a number parameter
cout << "Number is: " << num; //prints 1
The performance of the class is pretty fast: everything is just a reference on the stack. And to save all the information I use an internal buffer of up to 5 arguments before it goes to heap allocation to decrease the size of every single object, but this can be easily changed.
Why isn't this syntax used more often, overloading operator,() to implement named parameters? Is it because of the potential performance penalty?
One other way is to use the named idiom:
object.name("my name").ref(num); //every object method returns a reference to itself, allow object chaining.
But, for me, overloading operator,() looks much more "modern" C++, as long you don't forget to uses double parentheses. The performance does not suffer much either, even if it is slower than a normal function, so is it negligible in most cases.
I am probably not the first one to come up with a solution like this, but why isn't it more common? I have never seen anything like the syntax above (my example) before I wrote a class which accepts it, but for me looks it perfect.