[vwnc] Fwd: Otago academic download of Cincom Smalltalk vw7.5nc

From: "Richard A. O'Keefe" <[hidden email]>

Date: April 21, 2008 8:48:48 PM EDT

To: [hidden email]

Subject: Otago academic download of Cincom Smalltalk vw7.5nc

Name: Dr Richard A. O'Keefe
Org: Computer Science Department, The University of Otago
Web: http://www.cs.otago.ac.nz/
E-mail: [hidden email]

There seems to be a bug in Collection>>groupedBy:
If the collection being grouped is "pluggable", as SortedCollection is,
the instance variables of the receiver are not copied to the new
collections.  In the case of SortedCollection, this results in the
new collections being sorted the wrong way.  Here is a simple example:

  a := SortedCollection withAll: (1 to: 20) sortBlock: [:x :y | x >= y].
"PrintIt shows
SortedCollection (20 19 18 17 16 15 14 13 12 11 10 9 8 7 6 5 4 3 2 1)"
  a groupedBy: [:x | x \\ 4]
"PrintIt shows
Dictionary (0 -> SortedCollection (4 8 12 16 20)
    1 -> SortedCollection (1 5 9 13 17)
    2 -> SortedCollection (2 6 10 14 18)
    3 -> SortedCollection (3 7 11 15 19))"

It's possible to fix this case by adding

SortedCollection>>
groupedBy: keyBlock
   "Same as Collection>>groupedBy: but converts the subcollections
    to collections just like the receiver, including sortblock."
    | result |
    result := Dictionary new.
    self do: [:each |
        (result   at: (keyBlock value: each)
                ifAbsentPut: [OrderedCollection new]
        ) addLast: each].
    result keysAndValuesDo: [:key :value |
        result at: key put: (
            (self copyEmpty: value size) addAll: value; yourself)].
           ^result

Presumably other collection types may be affected as well.