Re: [boost] [review] conversion - Vladimir's comments

Subject: Re: [boost] [review] conversion - Vladimir's comments
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2011-08-30 13:20:15

On 30/08/2011 17:44, Gordon Woodhull wrote:

>> template<  class Target, class Source>
>> Target explicit_convert_to( Source const&  u );

 From the descriptions I have read, it seems this library is essentially 
those two lines.

Why should two lines of basic and non-variable C++ code form a Boost 
library?

>> does not really work on a bigger scale. That does indeed work for *concrete* Target and Source types. However, when one tries to generalize (partially specialize) for a range of similar types, then I feel the framework easily falters. Namely, if I decide to specialize the above for a range of related Target types (say, string-related types) *and* separately specialize for a range of related Source types. Then compilation will fail if these two separate specializations happen to overlap for some Target-Source pair. That is not an academic case but concrete issues I faced with Convert. I'd expect it to be as relevant with Vicente's library.

An interesting point. You could use SFINAE, but that doesn't scale and 
requires all partial specializations to be mutually exclusive.

I happen to have a library to solve the problem of specializing a 
function template for a category of types with best-match selection.

It's essentially a formalized way to define tag hierarchies and macros 
to make n-ary tag dispatching transparent.

It is what Boost.SIMD and NT2 use to manage their many specializations 
for different types and extensions.

It will be proposed to Boost as a library of its own, named Boost.Dispatch.
(sorry for hijacking the thread and advertising my stuff)