Re: How to build a string on the fly, using std::ostringstream? [Reposting]

Brendan Miller wrote:
> People do a using std::swap before calling swap, because if there
> is no swap provided by ADL, then we want the default swap to be
> available.

There's an extra reason for "using std::swap" within the body of a swap
function. Suppose we'd add a swap member function to the latest version of
Vidar's StringBuilder, having an std::auto_ptr member (StringBuilder::s).
Suppose we would write (inline, within the struct definition):

   void swap(StringBuilder& arg)
   {
     swap(this->s, arg.s);  // compile error!!!
   }

You might expect ADL to find std::swap, because auto_ptr is inside the std
namespace. But instead, it wouldn't compile, because name lookup would
find
the member function itself and stop there. When adding "using std::swap",
the
member swap would be hidded, and std::swap would be found!

   void swap(StringBuilder& arg)
   {
     using std::swap;
     swap(this->s, arg.s);  // Okay!
   }

So now I don't understand why Vidar's StringBuilder::operator<< compiles
without the using declaration!!!

Vidar Hasfjord wrote:
....
>     struct StringBuilder
>     {
>       std::auto_ptr <std::ostringstream> s;
>
....
>       template <typename T>
>       inline StringBuilder& operator << (const T& v)
>       {
>         *s << v;
>         return *this;
>       }

Why doesn't StringBuilder::operator<< hide other operator<< functions,
called
within its own body???  I would expect to get a compile error from doing
"*s
<< v"!!!


Thanks again,

   Niels



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