[cfe-dev] Introducing attribute objc_pure_virtual_method

[David Chisnall]

On 30 Oct 2013, at 08:53, Jean-Daniel Dupas <devlists at shadowlab.org> wrote:

> My 2 cents (even if the feature does not end up in clang).
> The concept of "pure virtual" may be clear for people common from C++, but I dont think this is the right wording to choose for Objective-C.
> The Apple documentation never ever mentions the term virtual once for objective-c.  I think the word commonly used is "abstract" so a better name for this attribute could be objc_abstract_method .

And even that is quite rare.  A more common notion in Objective-C is a primitive method (e.g. -length and -characterAtIndex: in NSString), which is then used to implement all of the others and must be implemented in subclasses.

It would be interesting to have a language feature that can check these (and make them more obvious - I've seen numerous instances of people skim-reading documentation and not identifying all of the methods that they must implement).  It would be cleaner, from a documentation standpoint, to be able to mark a protocol that a class implemented as requiring reimplementation in all subclasses.  Then it could be something that was both obvious in the documentation and checkable in the compiler.

David