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 16:44:13

On Thu, Feb 26, 2009 at 12:07 PM, Stewart, Robert
<Robert.Stewart_at_[hidden]> wrote:
> On Thursday, February 26, 2009 3:03 PM
> Emil Dotchevski wrote:
>>
>> 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
>
> That's a bit unfair, don't you think?  I know that you only wish to support std::string conversions, but the more complex machinery shown in the latter variant supports open ended formatting options and various target types.

I understand that the design direction I would take for the framework
is different, but I think you're missing the point of my previous
message.

Let's assume that converting to all kinds of target types with
open-ended formatting options in a single convert<> function is
desirable. Within that assumption, we need to provide reasonable
support for the case when the conversion of an uuid object to
std::string requires no parameters.

You can do this by requiring uuid.hpp to include all kinds of headers
and template goodness, learn your complex argument forwarding
framework -or- you can design your framework in a way that allows it
to bind simple function declarations or even member functions and
expose them through the generic convert<> interface.

I prefer the latter. Do you really find this unfair?

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