Re: proposition to update the lexical_cast

From: rogeeff (rogeeff_at_[hidden])
Date: 2001-12-28 11:30:25

Hi,

It is strange that nobody showed any interest, considering amount of 
discuttion on the topic at the beggining of the year. Don't you think 
it would be good to make lexical_cast more flexible?

Gennadiy.

--- In boost_at_y..., "rogeeff" <rogeeff_at_m...> wrote:
> Hi, all
> 
> Recently I have used lexical_cast extensively. And I found it 
> disapointing that I can't make it more effitient in some particular 
> cases where it could be very simple. The only thing that I need is 
a 
> bit flexibility of lexical_cast implementation. So I end up with 
the 
> following implementation:
> 
> template<class Stream, class Source>
> static void default_upload_impl( Stream& interpreter, Source const& 
> arg )
> {
>     if( !(interpreter << arg) )
>         throw bad_lexical_cast();
> }
> 
> template<class Stream, class Target>
> static void default_unload_impl( Stream& interpreter, Target& 
result )
> {
>     if( !(interpreter >> result) ||
>         !(interpreter >> std::ws).eof())
>         throw bad_lexical_cast();
> }
> 
> template<class Source>
> struct lexical_cast_interpreter {
>     explicit        lexical_cast_interpreter( Source const& ){}
> 
>     void            upload( Source const& arg )              { 
> default_upload_impl( m_interpreter, arg ); }
> 
>     template<class Target>
>     void            unload( Target& result )                 { 
> default_unload_impl( m_interpreter, result ); }
> 
> private:
>     string_stream   m_interpreter;
> };
> 
> } // namespace detail
> 
> template<class Target,class Source>
> Target lexical_cast(Source const& arg)
> {
>     detail::lexical_cast_interpreter<Source> interpreter( arg );
> 
>     interpreter.upload( arg );
> 
>     Target result;
> 
>     interpreter.unload( result );
> 
>     return result;
> }
> 
> } // namespace boost
> 
> Now to speed up a lexical_cast from std::string I am able to write 
a 
> specialization:
> 
> namespae detail {
> 
> template<>
> struct lexical_cast_interpreter<std::string> {
>     explicit        lexical_cast_interpreter( std::string const& 
> arg ) 
>     : m_interpreter( arg.data(), arg.size() )               {}
> 
>     void            upload( std::string const& )            {}
> 
>     template<class Target>
>     void            unload( Target& result )                { 
> default_unload_impl( m_interpreter, result ); }
> 
> private:
>     in_string_stream m_interpreter;
> };
> 
> } // namespace detail
> 
> Code and small performance comparison program is located here:
> 
> 
http://groups.yahoo.com/group/boost/files/lexical_cast_propositions/pr
> oposition1.cpp
> 
> Regards,
> 
> Gennadiy.