My own Smalltalk library (and yes, I've tried to put it on github, I don't know what I'm doing wrong) includes Deque and BoundedDeque, both descendants of Collection. Using addLast/removeLast gives you a stack (use #last for peeking) Using addLast/removeFirst gives you a queue. (use #first for peeking) (1) I am puzzled why there are separate FIFO and LIFO classes rather than a single BoundedDeque. -- This has implications for performance. (2) I am puzzled why #withCapacity: is used rather than #new:, familiar from OrderedCollection. -- These two points together make it hard to just swap OrderedCollection and ?IFOBuffer. (3) I am puzzled why #clear is used instead of the familiar #removeAll. -- See note on question 2. (4) I am extremely puzzled why ALL, like ALL, of the internals of the data structure are exposed. Did encapsulation fall out of favour and I didn't get the memo? (5) It looks as though calling #capacity: at the wrong time can destroy the integrity of one of these containers, but there is nothing sayiing "don't do that". (6) I am puzzled that they are not Collections. (7) I am puzzled why trying to access an element in an empty buffer does not signal a CollectionIsEmpty exception -- Is this related to (6)? The structure, with two separate classes and key performance-essential methods being template methods, hurts performance by about a factor of two in my tests. Now Pharo has a design MOOC and if Stephane Ducasse says "this is great", these things that puzzle me must be good design. I would like to improve my skills, so *why* is this good design? (As it happens, I *have* had occasion to 'push' from both ends of a single Deque.) None of this is meant as criticism of the generosity or competence of the authors. It expresses genuine puzzlement. Like when I implemented deques I could not imagine not making them Collections. Principle of Least Surprise and all that. Maybe I should be thinking differently. On Fri, 27 Jun 2025 at 20:10, stephane ducasse via Pharo-users <pharo-users@lists.pharo.org> wrote:

Thanks this is great!

On 18 Jun 2025, at 12:13, Alok via Pharo-users <pharo-users@lists.pharo.org> wrote:

Hello Everyone, We're excited to share a new addition to the pharo-containers. An efficient Circular Buffer implementation, developed as part of Google Summer of Code 2025 project under the mentorship of Gordana Rakic and Sebastian Jordan Montaño.

This package provides fixed-size buffers supporting both FIFO (queue-style) and LIFO (stack-style) behavior. It’s designed for use cases such as streaming data, undo/redo functionality, chat or browser history & more.

You can find the repo here: Containers-Buffer The README includes usage examples, installation steps etc.

Feedback, suggestions, and contributions are very welcome ! ThankYou ! Alok Pathak GSoC'25 Contributor

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Ah, the astc copy you found is years out of date. And the deque.st you found has had several mistakes fixed since. Here's why it mattered to me that these data structures weren't Collections. I was writing my own testing and benchmarking code to explore these ones. They have #isEmpty, so naturally I used both #isEmpty and #notEmpty in my tests. Not collections, so #notEmpty isn't there. They have #do:. They don't have #print:, so I threw together some printing code using the conventional #do:separatedBy:. Not collections, so #do:separatedBy: isn't there. Throw in a few non-nil elements, check [b noneSatisfy: [:each | each isNil]] assert. Not collections, so #noneSatisfy: isn't there. Tried to preload a buffer with specified contents using #withAll:. Not a collection, so #withAll: isn't there. Tried to compare the result of a series of operations with the expected one. Not a collection, so #asArray isn't there. Now Collection is big. Collection selectors size ==> 201 Collection allSelectors size ==> 692 in Pharo 12. Collection selectors size ==> 403 Collection allSelectors size ==> 1091 in astc with everything included, including compatibility packages, and a lot of the methods in Collection don't make sense for all descendants. I've tried very very hard to reduce this in astc, so my Collection doesn't include #+ . Basically, in order to be a "good faith" Collection in astc, you have to be able to to #do: multiple times without changing the multiset of items reported and you have to report #size consistent with this. I finally understood why these buffers expose all their implementation details, and there is arguably an excellent reason for it. There is a question I would like advice about, and that's the best way (in Pharo) to accomplish the same purpose without exposing the implementation. Here's the reason. I think of unit tests as testing the externally visible behaviour of an object, so that unit tests should only use the public interface of the objects they're working with. One reason for this is that I want to be able to change the internal details completely without changing the tests. For example, another way to implement a deque is using a doubly linked list, and there's no reason that it couldn't be bounded, so a *FIFOBuffer might not *have* an elements array or a readIndex integer, and making such a change leaves the unit tests still useful. Well and good: there is *A* category of tests that can and should be restricted to the public interface. But the authors of these buffers went further. They decided to test that the operations do the right thing the right *way* and created further tests that check the internal state of a buffer after an operation. To do this, they need *access* to the internal state. It seems to me that there are three ways to do this. (1) Put the test code *inside* the class under test as an extension. Have the test code in the image only when testing. (2) Add the access-to-private-details methods in an extension, included in the image only when testing. (3) What the authors did: reveal all the implementation details to all the world all the time. A fourth theoretical possibility, providing the access-to-private-details methods to the test class(es) only, is easy in Eiffel but appears to be impossible in Smalltalk. At this point a confession is appropriate. While testing and benchmarking their code, I found a discrepancy between their results and mine, and it was MY code that was broken. (I had tested Deque, but didn't really care about BoundedDeque very much, so hadn't tested it very thoroughly.) My bug *was* revealed by a conventional public-interface-only test, but it would have been revealed quicker by a test-the-implementation test like theirs. So I doff my hat to the authors for their thoroughness. GIVEN then that testing the implementation as well as the interface is a good idea, which of the 3 approaches above is recommended? Is there a still better way? On Sun, 29 Jun 2025 at 16:18, stephane ducasse <stephane.ducasse@inria.fr> wrote:

Hi richard

BTW guille found your prolog bookon second hand :)

My own Smalltalk library (and yes, I've tried to put it on github, I don't know what I'm doing wrong)

If you want we can get with it. Just ask and we can do a videos sessions with zoom,m webex, team or whatever software.

includes Deque and BoundedDeque, both descendants of Collection. Using addLast/removeLast gives you a stack (use #last for peeking) Using addLast/removeFirst gives you a queue. (use #first for peeking)

I have found on my disc astc-1711 but I could not find them. Can you send us the files?

(1) I am puzzled why there are separate FIFO and LIFO classes rather than a single BoundedDeque. -- This has implications for performance. (2) I am puzzled why #withCapacity: is used rather than #new:, familiar from OrderedCollection.

Good point

-- These two points together make it hard to just swap OrderedCollection and ?IFOBuffer.

(3) I am puzzled why #clear is used instead of the familiar #removeAll. -- See note on question 2.

Good point this is nice for API with Collection.

(4) I am extremely puzzled why ALL, like ALL, of the internals of the data structure are exposed. Did encapsulation fall out of favour and I didn't get the memo? (5) It looks as though calling #capacity: at the wrong time can destroy the integrity of one of these containers, but there is nothing sayiing "don't do that". (6) I am puzzled that they are not Collections.

What do you mean. If this is that they do not inherit from Collection I can understand because the API of collection is large. Now Alok it would be good to look at ANSI and see a bit the protocol I attach ANSI

(7) I am puzzled why trying to access an element in an empty buffer does not signal a CollectionIsEmpty exception -- Is this related to (6)?

The structure, with two separate classes and key performance-essential methods being template methods, hurts performance by about a factor of two in my tests.

Now Pharo has a design MOOC and if Stephane Ducasse says "this is great", these things that puzzle me must be good design. I would like to improve my skills, so *why* is this good design? (As it happens, I *have* had occasion to 'push' from both ends of a single Deque.)

I say great because any effort is good, Then we can discuss. I’m currently running a summerschool in parallel to prepare several talks to ESUG and finishing the organisation and reviewing other code and more. :)

None of this is meant as criticism of the generosity or competence of the authors. It expresses genuine puzzlement. Like when I implemented deques I could not imagine not making them Collections. Principle of Least Surprise and all that. Maybe I should be thinking differently.

On Fri, 27 Jun 2025 at 20:10, stephane ducasse via Pharo-users <pharo-users@lists.pharo.org> wrote:

Thanks this is great!

On 18 Jun 2025, at 12:13, Alok via Pharo-users <pharo-users@lists.pharo.org> wrote:

Hello Everyone, We're excited to share a new addition to the pharo-containers. An efficient Circular Buffer implementation, developed as part of Google Summer of Code 2025 project under the mentorship of Gordana Rakic and Sebastian Jordan Montaño.

This package provides fixed-size buffers supporting both FIFO (queue-style) and LIFO (stack-style) behavior. It’s designed for use cases such as streaming data, undo/redo functionality, chat or browser history & more.

You can find the repo here: Containers-Buffer The README includes usage examples, installation steps etc.

Feedback, suggestions, and contributions are very welcome ! ThankYou ! Alok Pathak GSoC'25 Contributor

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Alok I found in http://www.cs.otago.ac.nz/staffpriv/ok/astc-1711.tar.gz  "File : deque.st SCCS : '@(#)2017/08/23 deque.st 1.41' Author : Richard A. O'Keefe Defines: Deque, a non-indexable double-ended queue. Testing: The Squeak version of this has been tested. " require: 'ansi.st' "Usage : If you want indexing, use OrderedCollection. If you want O(1) {add,remove}{First,Last}, use Deque. Here is the reason this class exists. Measurements were done in Squeak 3.10 on a 2.53 GHz 2-core intel Mac. Time millisecondsToRun: [|c| c := OrderedCollection withAll: (1 to: 50). 1 to: 100000 do: [:i | c addLast: c removeFirst]] => 412, or about 4.12 µsec per iteration. Time millisecondsToRun: [|c| c := Deque withAll: (1 to: 50). 1 to: 100000 do: [:i | c addLast: c removeFirst]] => 25, or about 0.25 µsec per iteration. Using Visual Works Non-Commercial on a 2.53 GHz 2-core intel Mac, OrderedCollection => 84 nsec per iteration Deque => 41 nsec per iteration. And 50 elements is not a very large queue size. This Smalltalk does not offer a Stack class. Use Deque with #addLast: for push and #removeLast for pop. This Smalltalk does not offer a Queue class. Use Deque with #addLast: for enter and #removeFirst for leave. In 2012 I added BoundedDeque. The Booch Components include a circular buffer. The Boost library includes a circular buffer. The difference between a circular buffer and a deque is that if you insert into a collection that already fills the underlying array, a deque grows to hold it but a circular buffer overwrites an existing element. This is just like the difference between a Heap and a BoundedHeap. There is one major difference between our BoundedDeques and Boost circular buffers: they are indexed and ours are not. Our {,Bounded}Deques are Collections but not SequencedReadableCollections. We could do that too, there is even a draft that does it, but it hardly seems worth while. This needs to be rewritten to use better names internally because it uses three separate metaphors: first -- last left -- right top -- bottom We should stick with one, and since the interface has to be first -- last that's what we should stick with. " Integer methods: amod: other [other integer_between: 1 and: (C: maxInt)] assert. ^(self - 1) \\ other + 1 Collection abstractSubclass: #AbstractDeque instanceVariableNames: 'array left right size capacity' unshared: 'array' "hints: 'array (Array) left (SmallInteger) right (SmallInteger) size (SmallInteger) capacity (SmallInteger)'" methods for: 'checking' invariant ^(array isMemberOf: Array) and: [ capacity = array size and: [ capacity > 0 and: [ (size integer_between: 0 and: capacity) and: [ (left integer_between: 1 and: capacity) and: [ right = (left + size - 1 amod: capacity) ]]]]] methods for: 'copying' pvtArray: anArray array := anArray. left := 1. right := capacity := size := anArray size. ^self , aCollection |a i| a := Array new: size + aCollection size. i := 0. self do: [:each | a at: (i := i + 1) put: each]. aCollection do: [:each | a at: (i := i + 1) put: each]. ^self pvtClone pvtArray: a pvtPostCopy array := array copy. species ^self class reverse "If it makes sense to have #reverseDo:, it makes sense to have #reverse." |a i| a := Array new: size. i := 0. self reverseDo: [:each | a at: (i := i + 1) put: each]. ^self pvtClone pvtArray: a inPlaceReverse |a b x y| a := left. b := right. 1 to: size // 2 do: [:i | x := array at: a. y := array at: b. array at: a put: y. array at: b put: x. a := a == capacity ifTrue: [1] ifFalse: [a + 1]. b := b == 1 ifTrue: [capacity] ifFalse: [b - 1]]. methods for: 'accessing' size ^size anyOne "As long as #anyOne and #removeAnyOne are consistent, this could in general answer _any_ element. However, to be used as intended in threads.st, it must answer the first element of a deque, the best element of a heap, or indeed any element of a set-like collection" ^self first first size = 0 ifTrue: [self pvtEmptyError]. ^array at: left firstSatisfies: aBlock ^self isEmpty ifTrue: [false] ifFalse: [aBlock value: self first] last size = 0 ifTrue: [self pvtEmptyError]. ^array at: right lastSatisfies: aBlock ^self isEmpty ifTrue: [false] ifFalse: [aBlock value: self last] methods for: 'adding' add: item "In order to work with SharedQueue, this must add the item at the end removeAnyOne doesn't remove from." ^self addLast: item add: item ifPresent: exceptionBlock "Identical to AbstractSetLikeCollection>>add:ifPresent:." "Not enormously useful, but it _is_ well defined." ^(self includes: item) ifTrue: [exceptionBlock optionalValue: item] ifFalse: [self add: item] addIfNotPresent: item "Identical to AbstractSetLikeCollection>>addifNotPresent:." <compatibility: #pharo> "Not enormously useful, but it _is_ well defined." ^self add: item ifPresent: [] addIfNotPresent: item ifPresentDo: aBlock "Identical to AbstractSetLikeCollection>>addifNotPresent:." <compatibility: #pharo> "Not enormously useful, but it _is_ well defined." ^self add: item ifPresent: aBlock add: item withOccurrences: n ^self addLast: item withOccurrences: n addAll: aCollection ^self addAllLast: (self pvtCopyOr: aCollection) addAll: aCollection collect: aBlock (self pvtCopyOr: aCollection) do: [:each | self addLast: (aBlock value: each)]. addAll: aSequence from: start to: stop aSequence from: start to: stop do: [:each | self addLast: each]. addAll: aCollection keysAndValuesCollect: aBlock aCollection keysAndValuesDo: [:key :value | self addLast: (aBlock value: key value: value)]. addAllFirst: aCollection (self pvtCopyOr: aCollection) reverseDo: [:each | self addFirst: each]. addAllFirst: aCollection collect: aBlock (self pvtCopyOr: aCollection) reverseDo: [:each | self addFirst: (aBlock value: each)]. addAllFirst: aCollection from: start to: finish (self pvtCopyOr: aCollection) from: start to: finish reverseDo: [:each | self addFirst: each]. addAllFirst: aCollection from: start to: finish collect: aBlock (self pvtCopyOr: aCollection) from: start to: finish reverseDo: [:each | self addFirst: (aBlock value: each)]. addAllLast: aCollection (self pvtCopyOr: aCollection) do: [:each | self addLast: each]. addAllLast: aCollection collect: aBlock (self pvtCopyOr: aCollection) do: [:each | self addLast: (aBlock value: each)]. addAllLast: aCollection from: start to: finish (self pvtCopyOr: aCollection) from: start to: finish do: [:each | self addLast: each]. addAllLast: aCollection from: start to: finish collect: aBlock (self pvtCopyOr: aCollection) from: start to: finish do: [:each | self addLast: (aBlock value: each)]. addFirst: item self subclassResponsibility. addLast: item self subclassResponsibility. addFirst: item withOccurrences: n (n integer_between: 0 and: (C: maxSize)) ifFalse: [self pvtCountError: n]. 1 to: n do: [:i | self addFirst: item]. addLast: item withOccurrences: n (n integer_between: 0 and: (C: maxSize)) ifFalse: [self pvtCountError: n]. 1 to: n do: [:i | self addLast: item]. methods for: 'removing' removeAll array atAllPut: nil. left := 1. right := capacity. size := 0. removeAnyOne "As long as #anyOne and #removeAnyOne are consistent, this could in general remove _any_ element. However, to be used as intended in threads.st, it must remove the first element of a deque, the best element of a heap, or indeed any element of a set-like collection" ^self removeFirst removeFirst |r| size = 0 ifTrue: [self pvtEmptyError]. size := size - 1. r := array at: left. "\ was r := array _extractAt: left." array at: left put: nil. "/ was r := array _extractAt: left." left := left < capacity ifTrue: [left + 1] ifFalse: [1]. ^r removeFirstIfAbsent: aBlock "Interface from Dolphin." ^self isEmpty ifTrue: [aBlock value] ifFalse: [self removeFirst] removeFirst: n "Could be more efficient." (n integer_between: 0 and: size) ifFalse: [self pvtCountError: n]. 1 to: n do: [:i | self removeFirst]. removeLast |r| size = 0 ifTrue: [self pvtEmptyError]. size := size - 1. r := array at: right. "\ was r := array _extractAt: right." array at: right put: nil. "/ was r := array _extractAt: right." right := right == 1 ifTrue: [capacity] ifFalse: [right - 1]. ^r removeLastIfAbsent: aBlock "Interface from Dolphin." ^self isEmpty ifTrue: [aBlock value] ifFalse: [self removeLast] removeLast: n "Could be more efficient." (n integer_between: 0 and: size) ifFalse: [self pvtCountError: n]. 1 to: n do: [:i | self removeLast]. removeEvery: item self inPlaceSelect: [:each | each ~= item]. remove: item ^self remove: item ifAbsent: [self pvtNotFoundError: item] remove: item ifAbsent: aBlock |found value| found := false. self inPlaceSelect: [:each | found or: [ each = item ifTrue: [found := true. value := each. false] ifFalse: [true]]]. ^found ifTrue: [value] ifFalse: [aBlock optionalValue: item optionalValue: self] removeAll: items items do: [:each | self remove: each]. methods for: 'enumerating' do: aBlock size = 0 ifTrue: [^self]. right < left ifFalse: [ array from: left to: right do: aBlock] ifTrue: [ array from: left to: capacity do: aBlock. array from: 1 to: right do: aBlock]. collect: aBlock ^(self copy) inPlaceCollect: aBlock; yourself inPlaceCollect: aBlock size = 0 ifTrue: [^self]. right < left ifFalse: [ "array from: left to: right inPlaceCollect: aBlock" left to: right do: [:i | array at: i put: (aBlock value: (array at: i))]] ifTrue: [ "array from: left to: capacity inPlaceCollect: aBlock." left to: capacity do: [:i | array at: i put: (aBlock value: (array at: i))]. "array from: 1 to: right inPlaceCollect: aBlock" 1 to: right do: [:i | array at: i put: (aBlock value: (array at: i))]]. inPlaceReject: aBlock ^self inPlaceSelect: [:each | (aBlock value: each) not] inPlaceSelect: aBlock |d| size = 0 ifTrue: [^self]. right < left ifFalse: [ d := 0. array from: left to: right do: [:each | (aBlock value: each) ifTrue: [ array at: (d := d + 1) put: each]]. array replaceFrom: d + 1 to: right withObject: nil. left := 1. right := size := d] ifTrue: [ d := capacity + 1. capacity to: left by: -1 do: [:i | |each| (aBlock value: (each := array at: i)) ifTrue: [ array at: (d := d - 1) put: each]]. array replaceFrom: left to: d - 1 withObject: nil. left := d. d := 0. array from: 1 to: right do: [:each | (aBlock value: each) ifTrue: [ array at: (d := d + 1) put: each]]. array replaceFrom: d + 1 to: right withObject: nil. right := d. size := capacity - left + 1 + right]. removeAllSuchThat: aBlock ^self inPlaceReject: aBlock removeAllSuchThat: aBlock returnElements: aBoolean ^aBoolean ifTrue: [|r| r := self class new: self size. self inPlaceReject: [:each | (aBlock value: each) and: [r addLast: each. true]]. r] ifFalse: [self inPlaceReject: aBlock. nil] select: aBlock ^(self copy) inPlaceSelect: aBlock; yourself reverseDo: aBlock size = 0 ifTrue: [^self]. right < left ifFalse: [ array from: left to: right reverseDo: aBlock] ifTrue: [ array from: 1 to: right reverseDo: aBlock. array from: left to: capacity reverseDo: aBlock]. methods for: 'enumerating with two collections' "Sequences have a whole lot of <seq1> with: <seq2> <enum....> methods that iterate over two sequences in parallel. While deques may not be indexed, they *are* ordered in the same way that sequences are. The definitions here work whether the other collection is a sequence or a deque. The definitions in collections.st only work when the other collection is indexable. In fact, Deques *could* be indexable. Since the index of any element is constantly changing, that didn't seem like a good idea, and I certainly didn't want to drag in all the other sequence operations like #keysAndValuesDo:. It would be nice to have an AbstractSequenceLike class with AbstractDeque and AbstractSequence as subclasses, but that would clash with the AbstractKeyedCollection class. So currently deque1 with: deque2 do: aBlock -- works deque1 with: sequence2 do: aBlock -- works sequence1 with: sequence2 do: aBlock -- works sequence1 with: deque2 do: aBlock -- fails The reason the sequence methods require the other collection to be a sequence is so that the list case will work well. But list1 with: array2 do: aBlock -- fast array1 with: list2 do: aBlock -- slow so it need not be a problem. We just need to overide #with:do: in List as well. " with: aSequence collect: aBlock |a i j| a := Array new: size. i := left - 1. j := 0. aSequence do: [:each | i := i == capacity ifTrue: [1] ifFalse: [i + 1]. a at: (j := j + 1) put: (aBlock value: (array at: i) value: each)]. ^self pvtClone pvtArray: a with: aSequence do: aBlock |i| aSequence size = size ifFalse: [self pvtSizeMismatch: aSequence]. i := left - 1. aSequence do: [:each | i := i == capacity ifTrue: [1] ifFalse: [i + 1]. aBlock value: (array at: i) value: each]. with: aSequence allSatisfy: aBlock self with: aSequence do: [:x :y | (aBlock value: x value: y) ifFalse: [^false]]. ^true with: aSequence anySatisfy: aBlock self with: aSequence do: [:x :y | (aBlock value: x value: y) ifTrue: [^true]]. ^false with: aSequence noneSatisfy: aBlock self with: aSequence do: [:x :y | (aBlock value: x value: y) ifTrue: [^false]]. ^true with: aSequence oneSatisfies: aBlock |r| r := false. self with: aSequence do: [:x :y | (aBlock value: x value: y) ifTrue: [ r ifTrue: [^false] ifFalse: [r := true]]]. ^r methods for: 'streams' atEnd ^self isEmpty next ^self removeFirst nextPut: item self addLast: item. class methods for: 'instance creation' new ^self new: 4 new: size ^(self basicNew) pvtArray: (Array new: size); removeAll; yourself new: size atAllPut: item ^(self basicNew) pvtArray: ((Array new: size) atAllPut: item; yourself); yourself with: a1 ^self basicNew pvtArray: ( Array with: a1) with: a1 with: a2 ^self basicNew pvtArray: ( Array with: a1 with: a2) with: a1 with: a2 with: a3 ^self basicNew pvtArray: ( Array with: a1 with: a2 with: a3) with: a1 with: a2 with: a3 with: a4 ^self basicNew pvtArray: ( Array with: a1 with: a2 with: a3 with: a4) with: a1 with: a2 with: a3 with: a4 with: a5 ^self basicNew pvtArray: ( Array with: a1 with: a2 with: a3 with: a4 with: a5) with: a1 with: a2 with: a3 with: a4 with: a5 with: a6 ^self basicNew pvtArray: ( Array with: a1 with: a2 with: a3 with: a4 with: a5 with: a6) withAll: aCollection ^self basicNew pvtArray: ( Array withAll: aCollection) withAll: aCollection collect: aBlock ^self basicNew pvtArray: ( Array withAll: aCollection collect: aBlock) withAll: aCollection keysAndValuesCollect: aBlock ^self basicNew pvtArray: ( Array withAll: aCollection keysAndValuesCollect: aBlock) withAll: collection1 with: collection2 collect: aBlock ^self basicNew pvtArray: ( Array withAll: collection1 with: collection2 collect: aBlock) withAll: aCollection from: start to: stop ^self basicNew pvtArray: ( Array withAll: aCollection from: start to: stop) withAll: aCollection from: start to: stop collect: aBlock ^self basicNew pvtArray: ( Array withAll: aCollection from: start to: stop collect: aBlock) "How about rotateFirstToLast self addLast: self removeFirst rotateFirstToLast: n n timesRepeat: [self rotateFirstToLast] rotateLastToFirst self addFirst: self removeLast rotateLastToFirst: n n timesRepeat: [self rotateLastToFirst] but done more efficiently? " AbstractDeque subclass: #Deque methods for: 'adding' pvtGrowAtTopBy: amount |newArray| capacity := size + amount. newArray := Array new: capacity. 1 < size ifTrue: [ right < left ifTrue: [newArray replaceFrom: 1 to: size - right with: array startingAt: left. newArray replaceFrom: size - right + 1 to: size with: array startingAt: 1] ifFalse: [newArray replaceFrom: 1 to: size with: array startingAt: left]] ifFalse: [ 0 < size ifTrue: [newArray at: 1 put: (array at: left)]]. left := 1. right := size = 0 ifTrue: [capacity] ifFalse: [size]. array := newArray. pvtGrowAtBottomBy: amount |newArray| capacity := size + amount. newArray := Array new: capacity. right < left ifTrue: [newArray replaceFrom: amount + 1 to: capacity - right with: array startingAt: left. newArray replaceFrom: capacity - right + 1 to: capacity with: array startingAt: 1] ifFalse: [newArray replaceFrom: amount + 1 to: capacity with: array startingAt: left]. right := capacity. left := size = 0 ifTrue: [1] ifFalse: [capacity - size + 1]. array := newArray. addAllFirst: aCollection |n i| n := aCollection size. size + n > capacity ifTrue: [self pvtGrowAtBottomBy: n]. size := size + n. left := left - n. left < 1 ifTrue: [left := left + capacity]. i := left. aCollection do: [:each | array at: i put: each. i := i < capacity ifTrue: [i + 1] ifFalse: [1]]. addFirst: item size < capacity ifFalse: [self pvtGrowAtBottomBy: size + 1]. size := size + 1. left := left == 1 ifTrue: [capacity] ifFalse: [left - 1]. array at: left put: item. addFirst: item withOccurrences: n (n integer_between: 0 and: (C: maxSize)) ifFalse: [self pvtCountError: n]. size + n > capacity ifTrue: [self pvtGrowAtBottomBy: n]. size := size + n. 1 to: n do: [:i | left := 1 < left ifTrue: [left - 1] ifFalse: [capacity]. array at: left put: item]. addAllLast: aCollection |n i| n := aCollection size. size + n > capacity ifTrue: [self pvtGrowAtTopBy: n]. size := size + n. i := right. aCollection do: [:each | i := i < capacity ifTrue: [i + 1] ifFalse: [1]. array at: i put: each]. right := i. addLast: item size < capacity ifFalse: [self pvtGrowAtTopBy: size + 1]. size := size + 1. right := right < capacity ifTrue: [right + 1] ifFalse: [1]. array at: right put: item. addLast: item withOccurrences: n (n integer_between: 0 and: (C: maxSize)) ifFalse: [self pvtCountError: n]. size + n > capacity ifTrue: [self pvtGrowAtTopBy: n]. size := size + n. 1 to: n do: [:i | right := right < capacity ifTrue: [right + 1] ifFalse: [1]. array at: right put: item]. rehash ^self rehash: size rehash: n |newCapacity| newCapacity := n max: size. newCapacity = capacity ifFalse: [ |a d| a := Array new: newCapacity. d := 0. self do: [:each | a at: (d := d + 1) put: each]. array := a. left := 1. right := size]. AbstractDeque subclass: #BoundedDeque methods: addFirst: item left := left == 1 ifTrue: [capacity] ifFalse: [left - 1]. array at: left put: item. size == capacity ifFalse: [size := size + 1]. addLast: item right := right == capacity ifTrue: [1] ifFalse: [right + 1]. array at: right put: item. size == capacity ifFalse: [size := size + 1]. require: 'store-deque.st' if: 'store.st'

On 27 Jun 2025, at 12:23, Richard O'Keefe via Pharo-users <pharo-users@lists.pharo.org> wrote:

My own Smalltalk library (and yes, I've tried to put it on github, I don't know what I'm doing wrong) includes Deque and BoundedDeque, both descendants of Collection. Using addLast/removeLast gives you a stack (use #last for peeking) Using addLast/removeFirst gives you a queue. (use #first for peeking)

(1) I am puzzled why there are separate FIFO and LIFO classes rather than a single BoundedDeque. -- This has implications for performance. (2) I am puzzled why #withCapacity: is used rather than #new:, familiar from OrderedCollection. -- These two points together make it hard to just swap OrderedCollection and ?IFOBuffer. (3) I am puzzled why #clear is used instead of the familiar #removeAll. -- See note on question 2. (4) I am extremely puzzled why ALL, like ALL, of the internals of the data structure are exposed. Did encapsulation fall out of favour and I didn't get the memo? (5) It looks as though calling #capacity: at the wrong time can destroy the integrity of one of these containers, but there is nothing sayiing "don't do that". (6) I am puzzled that they are not Collections. (7) I am puzzled why trying to access an element in an empty buffer does not signal a CollectionIsEmpty exception -- Is this related to (6)?

The structure, with two separate classes and key performance-essential methods being template methods, hurts performance by about a factor of two in my tests.

Now Pharo has a design MOOC and if Stephane Ducasse says "this is great", these things that puzzle me must be good design. I would like to improve my skills, so *why* is this good design? (As it happens, I *have* had occasion to 'push' from both ends of a single Deque.)

None of this is meant as criticism of the generosity or competence of the authors. It expresses genuine puzzlement. Like when I implemented deques I could not imagine not making them Collections. Principle of Least Surprise and all that. Maybe I should be thinking differently.

On Fri, 27 Jun 2025 at 20:10, stephane ducasse via Pharo-users <pharo-users@lists.pharo.org> wrote:

...

Thanks this is great!

On 18 Jun 2025, at 12:13, Alok via Pharo-users <pharo-users@lists.pharo.org> wrote:

Hello Everyone, We're excited to share a new addition to the pharo-containers. An efficient Circular Buffer implementation, developed as part of Google Summer of Code 2025 project under the mentorship of Gordana Rakic and Sebastian Jordan Montaño.

This package provides fixed-size buffers supporting both FIFO (queue-style) and LIFO (stack-style) behavior. It’s designed for use cases such as streaming data, undo/redo functionality, chat or browser history & more.

You can find the repo here: Containers-Buffer The README includes usage examples, installation steps etc.

Feedback, suggestions, and contributions are very welcome ! ThankYou ! Alok Pathak GSoC'25 Contributor

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73 "If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Thnx a lot Richard for such great feedback. We'll definitely update the repo with all the necessary changes. Thanks Stephane for sharing all the resources. I'll definitely go through ANSI :) On Sun, 29 Jun, 2025, 13:40 Sebastian Jordan, <sebastian.jordan@inria.fr> wrote:

Hello Richard,

Thanks for your feedback. Just for context we are doing this project for the Google Summer of Code. I agree that the buffer should be polymorphic with the OrderedCollection. Yes, we should signal empty collection when accesing an empty buffer (7)

We will rok on that and come back to you Sebastian

Le 27 juin 2025 à 12:23, Richard O'Keefe via Pharo-users < pharo-users@lists.pharo.org> a écrit :

My own Smalltalk library (and yes, I've tried to put it on github, I don't know what I'm doing wrong) includes Deque and BoundedDeque, both descendants of Collection. Using addLast/removeLast gives you a stack (use #last for peeking) Using addLast/removeFirst gives you a queue. (use #first for peeking)

(1) I am puzzled why there are separate FIFO and LIFO classes rather than a single BoundedDeque. -- This has implications for performance. (2) I am puzzled why #withCapacity: is used rather than #new:, familiar from OrderedCollection. -- These two points together make it hard to just swap OrderedCollection and ?IFOBuffer. (3) I am puzzled why #clear is used instead of the familiar #removeAll. -- See note on question 2. (4) I am extremely puzzled why ALL, like ALL, of the internals of the data structure are exposed. Did encapsulation fall out of favour and I didn't get the memo? (5) It looks as though calling #capacity: at the wrong time can destroy the integrity of one of these containers, but there is nothing sayiing "don't do that". (6) I am puzzled that they are not Collections. (7) I am puzzled why trying to access an element in an empty buffer does not signal a CollectionIsEmpty exception -- Is this related to (6)?

The structure, with two separate classes and key performance-essential methods being template methods, hurts performance by about a factor of two in my tests.

Now Pharo has a design MOOC and if Stephane Ducasse says "this is great", these things that puzzle me must be good design. I would like to improve my skills, so *why* is this good design? (As it happens, I *have* had occasion to 'push' from both ends of a single Deque.)

None of this is meant as criticism of the generosity or competence of the authors. It expresses genuine puzzlement. Like when I implemented deques I could not imagine not making them Collections. Principle of Least Surprise and all that. Maybe I should be thinking differently.

On Fri, 27 Jun 2025 at 20:10, stephane ducasse via Pharo-users <pharo-users@lists.pharo.org> wrote:

Thanks this is great!

On 18 Jun 2025, at 12:13, Alok via Pharo-users < pharo-users@lists.pharo.org> wrote:

Hello Everyone, We're excited to share a new addition to the pharo-containers. An efficient Circular Buffer implementation, developed as part of Google Summer of Code 2025 project under the mentorship of Gordana Rakic and Sebastian Jordan Montaño.

This package provides fixed-size buffers supporting both FIFO (queue-style) and LIFO (stack-style) behavior. It’s designed for use cases such as streaming data, undo/redo functionality, chat or browser history & more.

You can find the repo here: Containers-Buffer The README includes usage examples, installation steps etc.

Feedback, suggestions, and contributions are very welcome ! ThankYou ! Alok Pathak GSoC'25 Contributor

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

ANSI is dead and this is good. Now this is interesting to learn from the analysis and the APIs.

On 30 Jun 2025, at 14:23, Richard O'Keefe <raoknz@gmail.com> wrote:

I have the final ANSI Smalltalk standard as published. I obviously cannot give it to you, but I *can* tell you that painfully few of the obvious errors in the 1.9 draft were corrected. For example, the DateAndTime class. The basic idea is sound, but we are told that the range of zone offsets is -12 hours to +12 hours. Well, I live in a country where the local time is UTC+13 hours for half the year and part of the country gets up to UTC+13 hours 45 minutes. Then there's the Line Islands that get up to +14 hours... Worse than that, the operations on DateAndTime literally *cannot* be implemented as specified, as they require you to know the leap second rules for thousands of years in the future. And the standard appears to assume that all places where the offset from UTC is such and such at one time has the same offset at all times. It sort of muddles up time zones with zone OFFSETS and then forgets about zones. The standard also suffers from being pre-Unicode, so it effectively assumes that random access by bytes makes sense in external text files.

There's another problem with the standard, which is that nobody much seems to have care about it once they'd finished with it. Case in point: the way to open a file in ANSI Smalltalk is to send a message to FileStream. Note only did Squeak and Pharo never bother to implement the standard messages for this purpose, Pharo has even deleted the class.

I'll get back to this tomorrow but my battery is about to say bye-bye.

On Sun, 29 Jun 2025 at 23:29, Alok <zhalok24@gmail.com> wrote:

...

Thnx a lot Richard for such great feedback. We'll definitely update the repo with all the necessary changes.

Thanks Stephane for sharing all the resources. I'll definitely go through ANSI :)

On Sun, 29 Jun, 2025, 13:40 Sebastian Jordan, <sebastian.jordan@inria.fr> wrote:

...

Hello Richard,

Thanks for your feedback. Just for context we are doing this project for the Google Summer of Code. I agree that the buffer should be polymorphic with the OrderedCollection. Yes, we should signal empty collection when accesing an empty buffer (7)

We will rok on that and come back to you Sebastian

Le 27 juin 2025 à 12:23, Richard O'Keefe via Pharo-users <pharo-users@lists.pharo.org> a écrit :

My own Smalltalk library (and yes, I've tried to put it on github, I don't know what I'm doing wrong) includes Deque and BoundedDeque, both descendants of Collection. Using addLast/removeLast gives you a stack (use #last for peeking) Using addLast/removeFirst gives you a queue. (use #first for peeking)

(1) I am puzzled why there are separate FIFO and LIFO classes rather than a single BoundedDeque. -- This has implications for performance. (2) I am puzzled why #withCapacity: is used rather than #new:, familiar from OrderedCollection. -- These two points together make it hard to just swap OrderedCollection and ?IFOBuffer. (3) I am puzzled why #clear is used instead of the familiar #removeAll. -- See note on question 2. (4) I am extremely puzzled why ALL, like ALL, of the internals of the data structure are exposed. Did encapsulation fall out of favour and I didn't get the memo? (5) It looks as though calling #capacity: at the wrong time can destroy the integrity of one of these containers, but there is nothing sayiing "don't do that". (6) I am puzzled that they are not Collections. (7) I am puzzled why trying to access an element in an empty buffer does not signal a CollectionIsEmpty exception -- Is this related to (6)?

The structure, with two separate classes and key performance-essential methods being template methods, hurts performance by about a factor of two in my tests.

Now Pharo has a design MOOC and if Stephane Ducasse says "this is great", these things that puzzle me must be good design. I would like to improve my skills, so *why* is this good design? (As it happens, I *have* had occasion to 'push' from both ends of a single Deque.)

None of this is meant as criticism of the generosity or competence of the authors. It expresses genuine puzzlement. Like when I implemented deques I could not imagine not making them Collections. Principle of Least Surprise and all that. Maybe I should be thinking differently.

On Fri, 27 Jun 2025 at 20:10, stephane ducasse via Pharo-users <pharo-users@lists.pharo.org> wrote:

Thanks this is great!

On 18 Jun 2025, at 12:13, Alok via Pharo-users <pharo-users@lists.pharo.org> wrote:

Hello Everyone, We're excited to share a new addition to the pharo-containers. An efficient Circular Buffer implementation, developed as part of Google Summer of Code 2025 project under the mentorship of Gordana Rakic and Sebastian Jordan Montaño.

This package provides fixed-size buffers supporting both FIFO (queue-style) and LIFO (stack-style) behavior. It’s designed for use cases such as streaming data, undo/redo functionality, chat or browser history & more.

You can find the repo here: Containers-Buffer The README includes usage examples, installation steps etc.

Feedback, suggestions, and contributions are very welcome ! ThankYou ! Alok Pathak GSoC'25 Contributor

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73

"If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes

Stéphane Ducasse http://stephane.ducasse.free.fr 06 30 93 66 73 "If you knew today was your last day on earth, what would you do differently? ....ESPECIALLY if, by doing something different, today might not be your last day on earth.” Calvin & Hobbes