Re: [boost] [type_traits] adding is_less_comparable<T>, etc.

Subject: Re: [boost] [type_traits] adding is_less_comparable<T>, etc.
From: Stewart, Robert (Robert.Stewart_at_[hidden])
Date: 2009-09-01 16:18:51

vicente.botet wrote:
>
> As sugested by Steven and Robert, have you tried
>
> typedef char no;
> struct yes { no dummy[2]; };
>
> yes is_bool(bool);
> no is_bool(...);
> template < typename T, typename U >
> struct is_less_comparable_impl {
> static typename boost::remove_cv<T>::type &t ;
> static typename boost::remove_cv<U>::type &u ;
> static const bool value = sizeof(is_bool(t<u))==sizeof(yes) ;
> }

Right.  The following is what he needs, I think.  This compiles, but I didn't dig into the results to verify it.

   typedef char fail;
   struct pass { fail dummy[2]; };

   pass is_bool(bool);
   fail is_bool(...);

   template <class T>
   T
   make_a();

   template < typename T, typename U >
   struct is_less_comparable_impl
   {
      typedef typename boost::remove_cv<T>::type t;
      typedef typename boost::remove_cv<U>::type u;
      static const bool value = sizeof(is_bool(make_a<t>() < make_a<u>()))
         == sizeof(pass);
   };

_____
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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