Re: [boost] [lexical_cast] char types and UDTs

Subject: Re: [boost] [lexical_cast] char types and UDTs
From: Mathias Gaunard (mathias.gaunard_at_[hidden])
Date: 2012-04-12 07:19:41

On 11/04/12 19:57, Antony Polukhin wrote:

> But that is not an optimal solution.
> Optimal solution would look like (not tested, required just to get the idea):
>
>
>
> template<class Target, class Source>
>
> Target lexical_cast_ext(Source&&  s) {
>
>      Target t;
>
>      if (!::boost::try_lexical_cast(t, std::forward<Source>(s)))
> // No ADL
>          BOOST_LCAST_THROW_BAD_CAST(Source, Target);
>
>
>
>      return t; // RVO must be applied by compiler
>
> }
>
>
>
> template<class Target, class Source>
>
> bool try_lexical_cast_ext(Target&  t, Source&&  s) noexcept {
>
>      using namespace boost::detail; // For getting default
> `construct_lexical_cast_in_trait' and
> `construct_lexical_cast_out_trait'
>
>
>
>      const auto&  in =
> construct_lexical_cast_in_trait(std::forward<Source>(s)); // ADL
>
>      if (in.fail()) return false;
>
>
>
>      typedef boost::mpl::identity<Target>  target_tag;
>
>
>
>      // Must have up to 4 construct_lexical_cast_out_trait
>      // {with parameters const char*, const wchar_t*, const char16_t*,
> const char32_t*}
>
>      return construct_lexical_cast_out_trait(target_tag(), in.begin(),
> in.end()) // ADL
>
>          .assign_value(t);
>           // returns true if conversion is OK
>
> }
>
>
>
> User will need to add one `construct_lexical_cast_in_trait' and up to
> four `construct_lexical_cast_out_trait' functions to the namespace of
> user-defined class.
>
>
>
> This will allow us to :
>
> * get correct function pointers via&lexical_cast<Source, Target>;
> (lexical_cast overloading solution breaks that)
>
> * use stream operators<<  and>>  in default lexical_cast traits
>
> * tune lexical_cast for fast conversions to string
> types(deduce_char_traits<>  specializing solution does not solve that)
>
> * tune lexical_cast for fast conversions from string types(both
> solutions do not solve that)
>
> * convert from any type to any type through usage of any character
> type (both solutions do not solve that)
>
> * relax all the type requirements (current implementation does not allow that)
>
> * have a noexcept version (current implementation does not allow that)
>
>
>
> Any objections? Did I miss something except conversion tags for specifying base?

Why is lexical_cast so complicated and full and quirks?

All that stuff looks messy and over-engineered.