Re: Explicit specialization in non-namespace scope

From:
Thomas Maeder <maeder@glue.ch>
Newsgroups:
comp.lang.c++.moderated
Date:
Wed, 28 Mar 2007 10:45:32 CST
Message-ID:
<m2tzw5quvm.fsf@glue.ch>
"robert.caldecott" <robert.caldecott@gmail.com> writes:

I am getting a 'explicit specialization in non-namespace scope' error
with gcc when attempting to compile the following:

class foo
{
public:
   template <typename T>
   foo& operator<<(const T& t)
   {
     ...
     return *this;
   }

   // Specialization for std::string
   template <>
   foo& operator<<(const std::string& str)
   {
     ...
     return *this;
   }
};


gcc is correct. Member template specializations have to be made in the
namespace that the class belongs to.

The above compiles fine using MSC. It appears I can workaround this
issue by moving the template code outside of foo, e.g.:

class foo
{
public:
   ...
};

template <typename T>
foo& operator<<(foo& f, const T& t)
{
   ...
   return f;
}

// Specialization for std::string
template <>
foo& operator<<(foo& t, const std::string& str)
{
   ...
   return f;
}

Are there any other workarounds other than the one above? Is it MSC
or GCC at fault here? I have quite a lot of specialization code
that I need to port.


We are not talking about workarounds here, but fixes. This would be
the correct version of your original attempt:

class foo
{
  public:
    template <typename T>
    foo& operator<<(const T& t)
    {
      return *this;
    }
};

// Specialization for std::string
template <>
foo& foo::operator<<(const std::string& str)
{
  return *this;
}

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