Re: [Boost-users] [parameter] Parameter-Enabled Class Templates:combining keyword and deduction for the same parameter

27 Jul 2007


      JOAQUIN LOPEZ MU?Z wrote:
...
----- Mensaje original -----
De: Daniel Wallin 
Fecha: Viernes, Julio 20, 2007 0:11 am
Asunto: Re: [Boost-users] [parameter] Parameter-Enabled Class 
Templates:combining keyword and deduction for the same parameter
Para: boost-users@lists.boost.org
...
David Abrahams wrote:
...
on Thu Jul 19 2007, "JOAQUIN LOPEZ MU?Z"  wrote:
...
Just to be sure: so, given the parameter specification
requiredtag::T,F>,
Boost.Parameter matches it to T<X> even if X does *not* satisfy
F, correct?
That's the intention... although I can't promise SFINAE won't 
kick in
in some cases.
Joaquin was talking about class templates, so the above holds true.
SFINAE will kick in if you use the restriction mechanism for function
templates. The PP interface does that, so if you use that you can't
supply parameter types that doesn't match the predicate.
I've read this over and over and can't say whether you're correcting
Dave or me :( excuse my incompetence. So, given (in the context
of class template parameters)
requiredtag::T,F>,
can Boost.Parameter match it to T<X> even if X does *not*
satisfy F? Thank you!
Yes, that is correct. However, is you use `parameters::match<>` to
restrict a function template, SFINAE will kick in. For example:

  BOOST_PARAMETER_FUNCTION((void), f, tag,
    (deduced
      (required (x, (std::string)))
    )
  );

  f(x = 10); // no overload matches

-- 
Daniel Wallin
Boost Consulting
www.boost-consulting.com