friend template function syntax

From:

"James K. Lowden" <jklowden@speakeasy.net>

Newsgroups:

comp.lang.c++.moderated

Date:

Sun, 5 Feb 2012 00:29:31 -0800 (PST)

Message-ID:

<20120204180440.28d14de3.jklowden@speakeasy.net>

How does one declare a friend function of a template class? The code
below dates from 1999 but gcc 4.1.3 says e.g.

    declaration of 'operator==' as non-function
    expected ';' before '<' token

Not my style. I would declare these functions as members, and use
constant references. But it looks valid to me and presumably was, once
upon a time. Cf. http://pdos.csail.mit.edu/prolac/.

Many thanks.

--jkl

template <class C>
class IDCapsule {

  C *_c;

public:

  IDCapsule() : _c(0) { }
  IDCapsule(const C *c) : _c((C *)c) { }

  operator bool() const { return _c != 0; }
  int hashcode() const { return (int)_c; }

  C &operator*() const { return *_c; }
  C *operator->() const { return _c; }
  operator C *() const { return _c; }
  C *obj() const { return _c; }

  friend bool operator==<>(IDCapsule<C>, IDCapsule<C>);
  friend bool operator==<>(IDCapsule<C>, IDCapsule<C>);
  friend bool operator==<>(IDCapsule<C>, C*);
  friend bool operator==<>(IDCapsule<C>, const C*);
  friend bool operator!=<>(IDCapsule<C>, IDCapsule<C>);
  friend bool operator!=<>(IDCapsule<C>, C*);
  friend bool operator!=<>(IDCapsule<C>, const C*);

};

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