The Inbox: Collections-ul.933.mcz

Levente Uzonyi uploaded a new version of Collections to project The Inbox:
http://source.squeak.org/inbox/Collections-ul.933.mcz

==================== Summary ====================

Name: Collections-ul.933
Author: ul
Time: 31 March 2021, 2:17:52.141067 am
UUID: b290ad2c-2ed0-4d46-b2fe-12545bf5f31c
Ancestors: Collections-ul.932

- use #ofSize: instead of #new: in SequenceableCollection class >> new:streamContents:, so that it creates a stream on a non-empty collection even if the receiver is OrderedCollection.

=============== Diff against Collections-ul.932 ===============

Item was changed:
  ----- Method: SequenceableCollection class>>new:streamContents: (in category 'stream creation') -----
  new: newSize streamContents: blockWithArg
 
  | stream originalContents |
+ stream := WriteStream on: (self ofSize: newSize).
- stream := WriteStream on: (self new: newSize).
  blockWithArg value: stream.
  originalContents := stream originalContents.
+ ^originalContents size =  stream position
+ ifTrue: [ originalContents ]
+ ifFalse: [ stream contents ]!
- originalContents size =  stream position
- ifTrue: [ ^originalContents ]
- ifFalse: [ ^stream contents ]!

---

Hi Christoph,

On Sat, 1 May 2021, Thiede, Christoph wrote:

>
> Hi Levente,
>
>
> so what is now the official interface for creating a valid collection of any kind of a certain size n? Shall we always use #ofSize:? Is this something that should be documented in the release notes?

There's no such interface for "a valid collection of any kind", and it's
not possible to create one, because we have many different collections
with different properties.
For that reason, Collection doesn't implement #new:, however it inherits
the method from Behavior, but that is not ideal.

#new: is actually there to support variable classes, so it works well for
ArrayedCollections, which are variable classes.
Some collections, like Set, Heap, Dictionary, etc. use it to take a
desired initial capacity. Unfortunately, OrderedCollection also follows
that pattern.
Some collections cannot implement #new:, like Interval or CharacterSet.

To answer your question, for ArrayedCollections, the method you asked
about is #new:.
OrderedCollection is a resizable ArrayedCollection: the collection
an OrderedCollection encapsulates (array) is always an ArrayedCollection.
Its API is similar to ArrayedCollection's but it is not exactly the same.
#new: is different.

As I wrote in another email recently, #new: could have been implemented
to create a non-empty collection unless the argument is 0. But for some
reason it wasn't.

#ofSize:, according to its method comment, was created to work around
that difference:

  "Create a new collection of size n with nil as its elements.
  This method exists because OrderedCollection new: n creates an
  empty collection,  not one of size n."

IMO the best would be to eliminate that difference, but it may be too late
now, because that would involve breaking all programs having the snippet

  OrderedCollection new: x

There are 97 potential methods with that pattern in my Trunk image (two of
those are false positives: the implementors of #ofSize:):

CurrentReadOnlySourceFiles cacheDuring: [
  | regex |
  regex := ('({1})\\s+new\\:' format: { (OrderedCollection withAllSubclasses collect: #name) joinSeparatedBy: '|' }) asRegex.
  SystemNavigation browseAllSelect: [ :method |
  regex search: method getSource asString  ] ].


Levente