Re: [Boost-users] design question with using call_traits and functors

From: Nat Goodspeed (nat_at_[hidden])
Date: 2008-05-22 16:31:10

Hansi wrote:

> I want to make a functor which uses automatically an reference type if 
> the provided value isn't a pointer.
> 
> Now the only thing that I don't like very much is that the user has to 
> provide the template argument for setter. Is there some possibility to 
> solve it that the template argument is automatically deduced?
> Important is that I have to possible calls one when the value is 
> provided as value -> I need to have a reference parameter and the other 
> is when a pointer is provided.

The following works for me:

#include <iostream>
#include <boost/lexical_cast.hpp>

template<typename Value>
void Set(const std::string& newVal, Value* pVal)
{
     *pVal = boost::lexical_cast<Value>(newVal);
}

template<typename Value>
void Set(const std::string& newVal, Value& refVal)
{
     refVal = boost::lexical_cast<Value>(newVal);
}

int main(int argc, char *argv[])
{
     int target;
     Set("17", &target);
     std::cout << "Set(Value*) produced " << target << '\n';
     Set("34", target);
     std::cout << "Set(Value&) produced " << target << '\n';
     return 0;
}

If you want those overloaded template free functions to forward to a 
functor, that should be fine too: as you see, inside them you can 
explicitly name the inferred type.