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User's Guide to the GNU Objective-C Class Library

5.2 The design philosophy.

Objective-C is not Smalltalk. Differences that matter to the Collection heirarchy:

• There can be only one set of argument types with each selector. (For instance in Objective-C we can't have "-(double)data" and "-(char)data". I can't stand it when some library that I'm forced to load already defines a selector that I want to use with different types.) This isn't an issue in Smalltalk because everything is an object.

  I make the Collection method names a little more descriptive, while keeping them close to Smalltalk. (For instance I think there is a good reason for using "-addObject:" instead of "-add:")

• We will want collections of int's, float's, and other non-Objects. Using Objective C wrappers around these C primitive types (i.e. Integer and Float objects) is not an efficient enough option for all cases.

  We could create two parallel heirarchies, one for Objects and one for elements passed as void*, but since so much of the functionality overlaps, I have merged them, and it doesn't actually look all that bad.

• Objective C doesn't have Smalltalk Blocks.

  Passing pointers to functions is a reasonable substitute. This is made easier with gcc's nested functions and the LAMBDA() macro defined in coll/collstd.h.

• Smalltalk does automatic garbage collection; Objective C doesn't.

  I think it should be made obvious which methods allocate a new object. Hence "-shallowCopyAs:[Bag class]" instead of "as:[Bag class]".

• We have usable Collection classes (Set, Bag, Array, etc) with functionality matching Smalltalk's objects, but there are good reasons for not having the abstract superclass structure match Smalltalk exactly.

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