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

Subject: Re: [boost] Formal Review Request: Boost.Convert
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-02-27 14:14:49

On Friday, February 27, 2009 2:06 PM
Emil Dotchevski wrote:
> On Fri, Feb 27, 2009 at 10:52 AM, Stewart, Robert
> <Robert.Stewart_at_[hidden]> wrote:
> > On Friday, February 27, 2009 1:48 PM
> > Emil Dotchevski wrote:
> >> On Fri, Feb 27, 2009 at 5:30 AM, Stewart, Robert
> >> <Robert.Stewart_at_[hidden]> wrote:
> >> >
> >> > The framework uses IOStreams to do its work.  I believe the
> >> > conversion functionality for the uuid type is captured via:
> >> >
> >> >   namespace user
> >> >   {
> >> >      class uuid;
> >> >
> >> >      template <class Stream>
> >> >      Stream &
> >> >      operator <<(Stream &, uuid const &);
> >> >   }
> >>
> >> If operator<< was a reasonable to-string alternative, we
> >> wouldn't be
> >> needing a library for it.
> >
> > That is the purpose of the insertion operator: it produces
> > a character sequence from the right hand argument.
>
> No, its purpose is to implement dumping of objects in streams, in
> terms of other existing operator<< overloads. This can also be used to
> convert to string, but the streams framework is rather clumsy to use
> when you need a std::string.

I hope you're not being purposely obtuse.  I raised the insertion operator as the spelling of the hook for the library because the library will use a std::ostringstream to produce the (formatted) output.  Since UDTs frequently provide such an operator, the convert code will piggy back on those operators easily, thus turning them into a handy means of converting to a string.

> >> It is relevant, of course, and the framework should be able to
> >> automatically bind suitable operator<< overloads if they exist. It
> >> should also provide a generic operator<< overload that
> calls convert,
> >> so all types that integrate in the convert framework are
> automatically
> >> compatible with streams.
> >
> > The library's convert() should use a provided operator <<()
> > when available and the library should provide an operator
> > <<() that uses a provided convert() when available?  How will
> > that work?
>
> The former requires a bit more template kungfu but isn't a problem.
>
> The latter is easy, well, sort of, you need to use the correct target
> type for convert, but you get the idea:
>
> template <class Stream,class T>
> Stream & operator<<( Stream & s, T const & x )
> {
>   return s << convert<std::string>(x);
> }

My point was it was a loop.  How do you resolve it?

_____
Rob Stewart                           robert.stewart_at_[hidden]
Software Engineer, Core Software      using std::disclaimer;
Susquehanna International Group, LLP  http://www.sig.com

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