Template i operator ==

Cześć!

Analizuję bibliotekę C++ i natrafiłem na taki problem:

class Foo
{
public:
    template<typename _T1, typename _T2>
    inline bool
    operator==(const _T1&, const _T2&){
        return false;
    }
};

Wywala błąd:
'bool Foo::operator==(const _T1&, const _T2&)' must take exactly one argument

zaś new_allocator z tym nie ma problemów (na samym końcu w źródle):

namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
{
_GLIBCXX_BEGIN_NAMESPACE_VERSION

  using std::size_t;
  using std::ptrdiff_t;

  /**
   *  @brief  An allocator that uses global new, as per [20.4].
   *  @ingroup allocators
   *
   *  This is precisely the allocator defined in the C++ Standard. 
   *    - all allocation calls operator new
   *    - all deallocation calls operator delete
   *
   *  @tparam  _Tp  Type of allocated object.
   */
  template<typename _Tp>
    class new_allocator
    {
    public:
      typedef size_t     size_type;
      typedef ptrdiff_t  difference_type;
      typedef _Tp*       pointer;
      typedef const _Tp* const_pointer;
      typedef _Tp&       reference;
      typedef const _Tp& const_reference;
      typedef _Tp        value_type;

      template<typename _Tp1>
        struct rebind
        { typedef new_allocator<_Tp1> other; };

#if __cplusplus >= 201103L
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 2103. propagate_on_container_move_assignment
      typedef std::true_type propagate_on_container_move_assignment;
#endif

      new_allocator() _GLIBCXX_USE_NOEXCEPT { }

      new_allocator(const new_allocator&) _GLIBCXX_USE_NOEXCEPT { }

      template<typename _Tp1>
        new_allocator(const new_allocator<_Tp1>&) _GLIBCXX_USE_NOEXCEPT { }

      ~new_allocator() _GLIBCXX_USE_NOEXCEPT { }

      pointer
      address(reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }

      const_pointer
      address(const_reference __x) const _GLIBCXX_NOEXCEPT
      { return std::__addressof(__x); }

      // NB: __n is permitted to be 0.  The C++ standard says nothing
      // about what the return value is when __n == 0.
      pointer
      allocate(size_type __n, const void* = 0)
      { 
	if (__n > this->max_size())
	  std::__throw_bad_alloc();

	return static_cast<_Tp*>(::operator new(__n * sizeof(_Tp)));
      }

      // __p is not permitted to be a null pointer.
      void
      deallocate(pointer __p, size_type)
      { ::operator delete(__p); }

      size_type
      max_size() const _GLIBCXX_USE_NOEXCEPT
      { return size_t(-1) / sizeof(_Tp); }

#if __cplusplus >= 201103L
      template<typename _Up, typename... _Args>
        void
        construct(_Up* __p, _Args&&... __args)
	{ ::new((void *)__p) _Up(std::forward<_Args>(__args)...); }

      template<typename _Up>
        void 
        destroy(_Up* __p) { __p->~_Up(); }
#else
      // _GLIBCXX_RESOLVE_LIB_DEFECTS
      // 402. wrong new expression in [some_] allocator::construct
      void 
      construct(pointer __p, const _Tp& __val) 
      { ::new((void *)__p) _Tp(__val); }

      void 
      destroy(pointer __p) { __p->~_Tp(); }
#endif
    };

  template<typename _Tp>
    inline bool
    operator==(const new_allocator<_Tp>&, const new_allocator<_Tp>&)
    { return true; }
  
  template<typename _Tp>
    inline bool
    operator!=(const new_allocator<_Tp>&, const new_allocator<_Tp>&)
    { return false; }

_GLIBCXX_END_NAMESPACE_VERSION
} // namespace

O co chodzi?

Wersja "metoda klasy" przyjmuje 1 argument, wersja "globalna" przyjmuje 2.

twonek napisał(a):

Wersja "metoda klasy" przyjmuje 1 argument, wersja "globalna" przyjmuje 2.

Jak w takim razie new_allocator jest wersją "globalną"?

Dobra, widzę!
Myślałem że operatory są w klasie, źródła C++ są trochę nieczytelne i formatowanie jest trochę rozjechane.
Dzięki :)