Alp Mestan’s Corner

Hi all,

Maybe you already know this trick… Maybe not.

Maybe one day, you would have liked to write a functor with a total genericity…
Let’s say you have this functor.

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struct Printer
{
    void operator() (const MyClass& obj)
    {
        std::cout << obj.toString() << endl;
    }
};

Let’s imagine you have many other class that implements the toString() member function. Then, let’s try to add genericity to the previous code.

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template <class T>
struct Printer
{
    void operator() (const T& obj)
    {
        std::cout << obj.toString() << endl;
    }
};

Nice try… But if we want to call our functor, we must specify T at our Printer’s declaration ! That’s not what we want. In fact, it would be great not to specify explicitly what T is when calling declarating and calling a Printer.

The problem in the previous code is that we have added genericity at a too high level… Indeed, templatizing operator() is really enough !

Let’s take a look.

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struct Printer
{
    template <class T>
    void operator() (const T& obj)
    {
        std::cout << obj.toString() << endl;
    }
};

Now, you’ll be able to call our functor on any object that has a toString() member function, moreover without specifying explicitly its type.