Re: [boost] Formal Review Request: Boost.Convert

Subject: Re: [boost] Formal Review Request: Boost.Convert
From: Emil Dotchevski (emildotchevski_at_[hidden])
Date: 2009-02-26 15:02:59

On Thu, Feb 26, 2009 at 8:18 AM, Andrey Semashev
<andrey.semashev_at_[hidden]> wrote:
> Emil Dotchevski wrote:
>> Anyway, another question: is there a way to make operator() not be a
>> template?
> It should be doable if you only need to receive the "source" argument to
> convert from. But if you want other arguments as well, I can't figure out
> how to do it without a template, unless to resort to type erasure.

Well, one way to take arguments is to tell the compiler that your
function or operator() takes arguments, right?

std::string operator()( uuid const & value, int arg1, float arg2 );

C++ was type-safe even before templates were introduced. :)

> If you're trying to extract the conversion code into a separate TU, then you
> can leave the operator() a template, so it is able to transform the named
> arguments pack into a call of a non-template function with positional
> arguments only.

I'm not trying to extract the conversion code into a separate TU, I'm
trying to justify putting it in the header. :)

If I'm the maintainer of class uuid and I am asked to provide a
to-string conversion, you'll find it very difficult to convince me
that it makes sense to replace this:

#include <string>

namespace user {
  class uuid;
  std::string to_string( uuid const & );
}

with all of this:

#include <boost/mpl/and.hpp>
#include <boost/mpl/bool.hpp>
#include <boost/typeof/typeof.hpp>
#include <boost/utility/enable_if.hpp>
#include <boost/type_traits/is_integral.hpp>
#include <boost/parameter/keyword.hpp>

#include <kitchen_sink.hpp>

namespace user {

struct uuid
{
    unsigned char value_[16];
};

struct uuid_to_string_tag {};

template< typename ToT >
typename boost::enable_if<
    boost::conversion::is_string< ToT >,
    uuid_to_string_tag
>::type get_conversion_tag(uuid*, ToT*);

} // namespace user

namespace boost {

namespace conversion {

template< typename ToT >
struct converter_impl< ToT, user::uuid_to_string_tag >
{
    typedef ToT result_type;

    template< typename ArgsT >
    ToT operator() (ArgsT const& args) const
    {
        ....
    }
};

} // namespace conversion

} // namespace boost

Emil Dotchevski
Reverge Studios, Inc.
http://www.revergestudios.com/reblog/index.php?n=ReCode