[Openmcl-devel] packages and Objective-C

R. Matthew Emerson rme at thoughtstuff.com
Mon Oct 29 10:42:22 PDT 2007

When programming in Objective-C, Apple recommends that programmers use  
a prefix when naming classes (and other things).  See the link below.


Objective-C has no packages or namespaces, so this prefixing technique  
is a way to help avoid symbol collisions.  In Common Lisp, though, we  
have the package system.

The question then, is can we/should we do anything about mapping the  
package system onto Objective-C classes in the bridge?

As a proof-of-concept, I made modifications to the current bridge to  
prefix a form of the package name onto Objective-C class names.

The basic idea is to find the symbol's home package, convert dashes in  
the (shortest) package name to underbars, and stick that onto the  
front of the class name with two underbars.

So, this sort of thing:

(in-package "CCL")

(defclass lisp-preferences-panel (ns:ns-panel)
   (:metaclass ns:+ns-object))

(objc:defmethod #/sharedPanel ((self +lisp-preferences-panel))

(objc:defmethod (#/show :void) ((self lisp-preferences-panel))

Gets mapped into this:

  +[CCL__LispPreferencesPanel sharedPanel]
  -[CCL__LispPreferencesPanel show]

As another example. suppose you've got a package "COOL-STUFF".  You  
define cool-stuff::my-
great-class in that package, and it gets turned into  

(Of course, it might be possible to come up with some other, perhaps  
better, sort of name mangling scheme, but I just picked this one  
because it was easy.)

It's necessary to stick to valid C identifiers for class names because  
Interface Builder won't let you enter any other characters.

Now, there's little hope that this sort of ad hoc scheme will cover  
every possible contingency.  For example, it won't work with packages  

But, I think this, or something like this, could be made to work in  
the usual case.

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