Re: [boost] [conversion] review

Subject: Re: [boost] [conversion] review
From: Gordon Woodhull (gordon_at_[hidden])
Date: 2011-08-30 10:41:18

Hi Phil,

On Aug 29, 2011, at 6:09 PM, "Phil Endecott" <spam_from_boost_dev_at_[hidden]> wrote:
> Gordon Woodhull wrote:
>> If I had to write a conversion function, I would rather write it as an overload of a general-purpose converter, rather than giving it some ugly typeA2TypeB name.
> 
> Why is e.g. rgb_to_cmyk() "ugly"?
> 
> Is it because it is C, and C syntax is ancient history that must be purged from modern C++?

I have nothing against C.  (I have learned a few techniques from C that got lost in C++'s rush to object orientation.) 

It's probably a matter of personal taste, but once I know that a function is a conversion from X to Y any other names are just noise to me.

Having a unique name means (to me) that there might be many other ways of doing the same thing, and I'm not sure if I've chosen the right one. Going through a generic function means I or someone has chosen the best way and can replace it if they want. 

E.g. convert strings to & fro types with a generic interface where you could switch in either lexical_cast or coerce and evaluate their performance.

Granted this is not as strong an argument as if we had a real use case for generic conversion itself.  

E.g. why write

template<typename X, typename Y>
void do_something_amazing(Y const& Y) {
   X x;
   // If only I could convert Y to X... aha!
   x = boost::conversion::convert_to<X>(y);
   // ... some magic occurs
}

?

The only example I could come up with is implementing Perl-like scalars in C++ but I have no idea why you'd want to do that.  So I'm hoping that some people who have tried to use lexical_cast for general type-to-type conversion will speak up.

I think Vicente's argument is much like my "personal taste" argument above: he would just rather have a single function than many.  Especially when you consider that there's combinatorial complexity in the number of interchangeable types.

Cheers
Gordon