Re: [boost] [mpl] Using apply with gcc error

3 Feb 2011

      On 2/3/2011 6:08 PM, Larry Evans wrote:
...
On 02/03/11 17:02, Steven Watanabe wrote:
...
AMDG
On 2/3/2011 2:42 PM, Edward Diener wrote:
...
Compiling this code with gcc:
#include<boost/config.hpp>
#include<boost/mpl/apply.hpp>
template
<
class MF,
class T
...
struct myMF :
boost::mpl::apply<MF,T>
{
BOOST_STATIC_CONSTANT(bool,value=type::value);
};
int main()
{
return 0;
}
Gives:
"gcc.compile.c++
..\..\..\bin.v2\libs\tti\test\TestMFHasTypeMFC.test\gcc-mingw-4.5.2\debug\TestMFHasTypeMFC.o
TestMFHasTypeMFC.cpp:18:5: error: 'type' has not been declared
gcc is correct.  Members of a dependent base class are
not visible in the derived class.  (This is necessary
to allow the template to be parsed before the template
arguments are known.).
Add
using typename boost::mpl::apply<MF,T>::type;
In Christ,
Steven Watanabe
_______________________________________________
That using works with clang++; however, my gcc (gcc4.5.1)
still doesn't like it:
make using
cat myMF.cpp
//Copied from post with headers:
/*
From: Edward Diener<eldiener@tropicsoft.com>
Newsgroups: gmane.comp.lib.boost.devel
Subject: [mpl] Using apply with gcc error
Date: Thu, 03 Feb 2011 17:42:44 -0500
Lines: 47
  */
#include<boost/config.hpp>
#include<boost/mpl/apply.hpp>
template
      <
      class MF,
      class T
      >
    struct myMF :
      boost::mpl::apply<MF,T>
      {
      using typename boost::mpl::apply<MF,T>::type;
      BOOST_STATIC_CONSTANT(bool,value=type::value);
      };
int main()
      {
      return 0;
      }
/home/evansl/download/llvm/svn/build/Debug+Asserts/bin/clang++ -c
-std=c++0x -U__GXX_EXPERIMENTAL_CXX0X__ -c myMF.cpp
/home/evansl/download/gcc/4.5.1-release/install/bin/g++ -c -Wall
-ftemplate-depth-300 -O0 -std=gnu++0x -c myMF.cpp
myMF.cpp:21:6: error: 'type' is not a class, namespace, or enumeration
make: [using] Error 1 (ignored)
Compilation finished at Thu Feb  3 17:04:44
I guess the easiest solution is to just give up the metafunction 
forwarding and have:

   template
     <
     class MF,
     class T
     >
   struct myMF
     {
     typedef typename boost::mpl::apply<MF,T>::type type;
     BOOST_STATIC_CONSTANT(bool,value=type::value);
     };

This seems to work everywhere.