__property keyword support in GCC

[Martin v. Loewis]

> Parsing the declaration of a property type is, as you say, relatively
> simple.  But the main work would be the appropriate handling of property
> symbols in all contexts, including all the contexts where they don't make
> sense (attempts to create pointers or references to a property, etc)

Just to extend this list somewhat: When defining the extension, you'll
have to explain:

- access control: if the property is private or protected, does it
  matter, or is it the access of the referred-to property that
  matters?

- inheritance 1: can the derived class redefine a property defined in
  the base?

- inheritance 2: can a property defined in a derived class refer to
  accessor functions in the base class?

- inheritance 3: can a property defined in the base class refer to
  accessor functions in the derived class (e.g if the accessor
  function is redefined)

- virtuality: If the accessor function is virtual, which function is
  invoked? Probably the one in the most-derived type. Is there a way
  to cancel virtual using qualification?

- typing: What is the type of the property? Probably the type of the
  accessor functions. Can those process different types (e.g. read
  returns one type, write consumes another)

- typing and overloading: If there is more than one accessor function
  with a given name, which one is selected?

- passing by reference: Is a property an lvalue, if it has read and
  write? If so, how exactly are accessor functions invoked?

- constness: If an object is const, does this affect availability of
  accessor functions? If so, how?

I guess there are more. I have no plans of implementing the feature,
so there is no real reason to explain all the details to me.

Regards,
Martin