"Lex Spoon" lex@cc.gatech.edu wrote: By the way, there is a nice generalization of the above with:foo: pattern. It looks like this: (firstArray with: secondArray) collect: [ :combo | combo first + combo second ] This use of #with: (which doesn't currently exist), is identical to ML and Haskel's "zip" function, and it allows you to use all of collect:, select:, reject:, do:, detect:, etc. without writing with:collect:, with:select:, with:reject:, etc. In brief, the presence of a "with" clause can be orthogonal to which collection operation is being used. Now it does exist. Note that it can be combined, so ((a with: b) with: (c with: d)) collect: [:combo | ... combo first first "a" ... ... combo first second "b" ... ... combo second first "c" ... ... combo second second "d" ... ] gives you iteration over four collections, should you want that.

'From Squeak2.8 of 13 June 2000 [latest update: #2359] on 4 September 2001 at 1:52:50 pm'! Magnitude subclass: #Pair instanceVariableNames: 'first second ' classVariableNames: '' poolDictionaries: '' category: 'Collections-Support'!

!Pair commentStamp: 'raok 9/4/2001 13:21' prior: 0! I represent an ordered pair of objects. Pairs exist to support iteration over two or more collections at once and have no semantics other than aggregation. As a rule, you should look for a problem-domain abstraction you can use rather than reusing me.

Pair first: x second: y makes a new Pair object. The obvious accessors are defined. Comparison is defined as ledxicographic comparison.

My instance variables 'first' and 'second' mean what they sound like. ! SequenceableCollection subclass: #PairedCollection instanceVariableNames: 'first second count size ' classVariableNames: '' poolDictionaries: '' category: 'Collections-Sequenceable'!

!PairedCollection commentStamp: 'raok 9/4/2001 13:45' prior: 0! I act like the sequence you would get by doing a with: b collect: [:x :y | Pair first: x second: y] except that I do not allocate a new array or ordered collection, nor do I create all the pairs straight away. I create pairs lazily, as they are needed. That means that previously generated pairs can be reclaimed by the garbage collector while you are still traversing me. The essence of a PairedCollection is to delegate accesses to the collections it is built from, so you are not allowed to change one.

(a with: b) collect: [:aPair| ... aPair first ... aPair second ...] is like a with: b collect: [:x :y| ... x ... y ...]!

!Pair methodsFor: 'comparing' stamp: 'raok 9/4/2001 13:25'! < aPair first < aPair first ifTrue: [^true]. aPair first < first ifTrue: [^false]. ^second < aPair second! !

!Pair methodsFor: 'comparing' stamp: 'raok 9/4/2001 13:24'! = aPair self species = aPair species ifFalse: [^false] ifTrue: [^first = aPair first and: [second = aPair second]]! !

!Pair methodsFor: 'comparing' stamp: 'raok 9/4/2001 13:26'! hash ^first hash "quick and dirty"! !

!Pair methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:21'! first ^first! !

!Pair methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:22'! first: anObject first _ anObject! !

!Pair methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:26'! first: x second: y first _ x. second _ y. ! !

!Pair methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:22'! second ^second! !

!Pair methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:23'! second: anObject second _ anObject ! !

!Pair class methodsFor: 'instance creation' stamp: 'raok 9/4/2001 13:28'! first: x second: y ^self new first: x second: y! !

!SequenceableCollection methodsFor: 'converting' stamp: 'raok 9/4/2001 13:49'! with: anotherCollection "answer a new PairedCollection for iteration" ^PairedCollection first: self second: anotherCollection! !

!PairedCollection methodsFor: 'private' stamp: 'raok 9/4/2001 13:44'! species "Answer the preferred class for reconstructing the receiver." ^Array! !

!PairedCollection methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:36'! at: anIndex ^Pair first: (first at: anIndex) second: (second at: anIndex)! !

!PairedCollection methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:36'! at: anIndex put: anObject self error: 'a PairdCollection cannot be changed' ! !

!PairedCollection methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:49'! first: aCollection second: anotherCollection aCollection size = anotherCollection size ifFalse: [self error: 'collection sizes must match']. first _ aCollection. second _ anotherCollection. size _ aCollection size. ^self! !

!PairedCollection methodsFor: 'accessing' stamp: 'raok 9/4/2001 13:35'! size ^size! !

!PairedCollection class methodsFor: 'instance creation' stamp: 'raok 9/4/2001 13:46'! first: aCollection second: anotherCollection ^self new first: aCollection second: anotherCollection! !