Re: [boost] An alternative approach to TypeErasure

Subject: Re: [boost] An alternative approach to TypeErasure
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2012-06-24 18:42:55

AMDG

On 06/24/2012 03:34 AM, Pyry Jahkola wrote:
> 
> Here's a somewhat shorter intro:
> 
> 1) Create a callable F by simply deriving it from poly::callable<F>:
> 
>    struct draw_ : poly::callable<draw_> {};
>    constexpr draw_ draw = {};
> 
> 2) Or use the convenience macro POLY_CALLABLE(name) to do the same:
> 
>    POLY_CALLABLE(to_string); // type `to_string_` and object `to_string`
> 
> 3) Overload your callables by overloading the function named `call`,
> with the callable as first argument:
> 
>    template <typename T>
>    void call(draw_, T const & x, std::ostream & out, std::size_t
> position) {
>        out << std::string(position, ' ') << x << std::endl;
>    }
> 

Some thoughts on this interface:

a) It's a bit more concise than my interface,
   but the difference isn't major.
b) ADL is less robust than class template
   specialization, since it can accidentally
   pull in unrelated functions that happen
   to have the same name.
c) Your function objects won't overload
   properly with ordinary functions, if,
   for example, someone has a function called
   draw or to_string that operates on his own
   type.

In Christ,
Steven Watanabe