a class-key must be declared when declaring a friend

The g++ compiler complains with this error when I declare a friend thusly:

friend MyClass;

instead of

friend class MyClass;

Why should the class keyword be required? (the Borland C++ compiler, BTW, does not require it.)

Couldn't the compiler simply look-up MyClass in the symbol table and tell it was declared as a class? (it is obviously doing the look-up anyway because it complains when MyClass it not declared)

It is not like it is making a forward declaration of the class: I still have to have either declared the class above or at least have forward declared it.

It would make sense to me (would be great actually) if

friend class MyClass;

makes a forward declaration if needed, otherwise it just seems like syntactic salt to me.

I have been merrily using friend statements without the class or struct keyword with no compiler complaints for almost 20 years. Is this something fairly new?

From stackoverflow

• To the point of your question, because it is the way ISO/IEC 14882:2003 specifies it (section 7.1.4). The friend construct is essentially specified as:

  friend <declaration>
  

  where <declaration> is the valid declaration of a class, struct, template, or function.

  Thus,

  MyClass;
  

  is not a valid declaration, whereas:

  class MyClass;
  

  or:

  struct MyClass;
  

  are.

  Idem for, correspondingly:

  friend class MyClass;
  

  or

  friend struct MyClass;
  

• I was surprised about this (and as a result deleted a previous incorrect answer). The C++03 standard says in 11.4:

  An elaborated-type-specifier shall be used in a friend declaration for a class.

  Then to make sure there's no misunderstanding, it footnotes that with:

  The class-key of the elaborated-type-specifier is required.

  GCC is the only compiler that I have that complains about the missing class-key, but it looks like other compilers are letting us get away with something non-standard...

  Now as for the rationale - you'd have to ask someone who knows more about compilers (or standards) than I do.