[Boost-bugs] [Boost C++ Libraries] #9436: Add predefined concept for contextual conversion to bool

Subject: [Boost-bugs] [Boost C++ Libraries] #9436: Add predefined concept for contextual conversion to bool
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2013-11-26 15:31:25

#9436: Add predefined concept for contextual conversion to bool
------------------------------+-----------------------------
 Reporter:  akrzemi1@…        |      Owner:  steven_watanabe
     Type:  Feature Requests  |     Status:  new
Milestone:  To Be Determined  |  Component:  type_erasure
  Version:  Boost 1.54.0      |   Severity:  Not Applicable
 Keywords:  operator bool()   |
------------------------------+-----------------------------
 One concept that is often useful in many types is a contextual conversion
 to bool. The following expressions should be valid with the concept:

 {{{
   if (o) {}
   if (!o) {}
   return bool(o);
 }}}


 Add a predefined concept that catches these requirement. A possible
 implementation:

 {{{
 namespace boost { namespace type_erasure {

 template<class T>
 struct testable
 {
   static bool apply(const T& arg)
   { return bool(arg); }
 };

 template<class T, class Base>
 struct concept_interface<testable<T>, Base, T> : Base
 {
   explicit operator bool () const
   { return call(testable<T>(), *this); }
 };
 }}
 }}}

-- 
Ticket URL: <https://svn.boost.org/trac/boost/ticket/9436>
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