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

Comment:

 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....

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/4462#comment:1>
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