Re: Meaning of methodReturnType values ?

[Richard Frith-Macdonald]

On Friday, June 15, 2001, at 02:26 PM, Laurent Julliard wrote:

> I'm playing with the GNUstep NSMethodSignature class. One of the method
> available in there is methodReturnType which is supposed to tell you
> about the type of the value returned by a method.
>
> Problem is: I couldn't find an include file where the meaning of the
> value returned by this method is explained. Actually it is supposed to
> return a string. I can print the string ok (look like "@8@4@:" for
> instance but I'm unable to make sense of it.
>
> Avi Bryant was kind enough to direct me to the ADC (Apple Developers
> Connection) site where there is some information about that but it
> doesn't seem to apply to GNUstep based on what I have observed so far.
> (see
> http://developer.apple.com/techpubs/macosx/Cocoa/Reference/Foundation/ObjC_classic/
> TypesAndConstants/FoundationTypesConstants.html
>
> and look for "ObjC Types" in the document)
>
>
> Any help/pointer or code samples would be really appreciated.

This stuff is defined by the compiler/runtime ... see onjc/objc-api.h

The NeXT/Apple book 'object oriented programming and the objective-c 
language' has a section on type encodings
(you can find various links to versions of this from the gnustep 
website).

Basically, for most purposes, ignore the numbers (they are for stack 
frame or register offsets and vary from machine to machine).

an '@' denotes an object,
an ':' denotes a selector
an 'i' is an integer
an 'I' is an unsigned integer
etc

Your example '@8@4@:' is a method returning an object, with two (hidden) 
arguments, the receiver, and the selector.
All methods will have a "@' and ':' for those two hidden arguments.

So '- (int) promote: (short)s;' would produce a type encoding string of 
'i@:s'