Re: [Boost-bugs] [Boost C++ Libraries] #10133: boost 1.55 breaks fusion map arrays

Subject: Re: [Boost-bugs] [Boost C++ Libraries] #10133: boost 1.55 breaks fusion map arrays
From: Boost C++ Libraries (noreply_at_[hidden])
Date: 2015-02-21 14:35:49

#10133: boost 1.55 breaks fusion map arrays
  Reporter: steven.seeger@… | Owner: djowel
      Type: Bugs | Status: new
 Milestone: To Be Determined | Component: fusion
   Version: Boost 1.55.0 | Severity: Regression
Resolution: | Keywords:

Comment (by Kohei Takahashi <flast@…>):

 I believe that it is not a fusion's bug.

 The constructor of `map` will take their arguments by Universal
 References, like `template <class... T> map(T &&...)`, to accept any types
 and any value categories, i.e. perfect forwarding.
 However, compiler cannot deduce the argument type from brace-enclosed
 initializer, see below.

 n3337 [] p.1 sais:

   If removing references
   and cv-qualifiers from P gives std::initializer_list<P 0 > for some P 0
 and the argument is an initializer
   list (8.5.4), then deduction is performed instead for each element of
 the initializer list, taking P 0 as a function
   template parameter type and the initializer element as its argument.
 Otherwise, an initializer list argument
   causes the parameter to be considered a non-deduced context (

 and [temp.deduct.type] p.4 sais:

   If a template parameter is used only in non-deduced
   contexts and is not explicitly specified, template argument deduction

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