[Help-smalltalk] meaning of Collection>>#copyEmpty:

[Stephen Compall]

copyEmpty: newSize 

    "Answer an empty copy of the receiver whose size is newSize" 

    ^self species new: newSize

Clearly, this has a different meaning when the argument to new: is 
treated as a capacity.  Furthermore, is #(nil nil nil nil nil) 
considered an empty Array?

I recently discovered that, due to this discrepancy, OrderedCollections 
cannot be used as contents of WriteStreams.  This isn't a major problem, 
because WriteStreams are after all designed to do the extra work that 
OrderedCollections do for you.  And Squeak, at least, shares this "feature".

I suppose my real question is whether this method can be rewritten in a 
way such that it would work sensibly for OrderedCollections without 
expanding the Collection protocol or doing explicit isKindOf: tests? -- 
not that I would recommend replacing this perfectly sensible 
implementation for such a silly purpose at all:

growCollection 

   "Private - Double the size of the collection or, if its size < 8, 

    grow it to 8 places" 

   | size | 

   size := collection size. 



   "Guess which collection is which :-)" 

   collection := ((collection copyEmpty: (size * 2 max: 8)) 

        replaceFrom: 1 to: collection size with: collection startingAt: 
1;
        yourself).

--
Stephen Compall
http://scompall.nocandysw.com/blog
##smalltalk,#gnu-smalltalk on Freenode IRC