Re: [Boost-bugs] [Boost C++ Libraries] #4462: make_signed is not SFINAE friendly

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #4462: make_signed is not SFINAE friendly
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2010-07-22 16:09:09

#4462: make_signed is not SFINAE friendly
  Reporter: 1czajnik@… | Owner: johnmaddock
      Type: Bugs | Status: closed
 Milestone: Boost 1.44.0 | Component: type_traits
   Version: Boost 1.44.0 | Severity: Problem
Resolution: invalid | Keywords: sfinae
Changes (by johnmaddock):

  * status: new => closed
  * resolution: => invalid


 This is not a bug - it's a deliberate design decision - make_signed is
 documented to require an integral or enumeration type as an argument (the
 latest draft of the std has the same restriction on std::make_signed).
 The static_assertion failure you're seeing is just make_signed asserting
 it's requirements.

 To do what you want, you would have to use boost::enable_if on the return
 type so that SFINAE fails if T is not an integer type, or else create your
 own thin wrapper about make_signed, something like:

 template <class T>
 struct make_signed_or_self
    typedef typename mpl::if_<is_integral<T>, make_signed<T>::type,
 T>::type type;

 All just typed in off the top of my head....

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