Thanks for this great explanation Henrik.
Nevertheless, my question is still valid. Why Set new will give me an internal
array of 5 elements while Set new: 1 will give me an internal array of 7
Shouldn’t Set new give an internal of 7 elements as it looks like the minimal
array size for a set?
Also I would expect Set new: 0 to give me an empty internal array. It
explicitly ask an empty Set. A further call to #add: will increase its size as
> Le 1 déc. 2016 à 13:25, Henrik Nergaard <henrik.nerga...@uia.no> a écrit :
> Hashed collections keep a portion of the available memory empty (usually 25%)
> as a partition mechanism to increase lookup speed.
> “Normal array”
> | col |
> col := Smalltalk allClassesAndTraits asArray.
> [ col includes: 8; includes: Morph ] bench. "'366.853 per second'"
> “Normal set ~75% load”
> | set |
> set := Smalltalk allClassesAndTraits asSet.
> [ set includes: 8; includes: Morph ] bench. "'4,700,967 per second'"
> “Set forced to have ~100% load”
> | array fullLoadSet |
> array := Smalltalk allClassesAndTraits asSet asArray , #(nil).
> fullLoadSet:= Set basicNew.
> instVarNamed: #array put: array;
> instVarNamed: #tally put: array size.
> [ fullLoadSet includes: 8; includes: Morph ] bench. "'215.157 per second'"
> Best regards,
> From: Pharo-dev [mailto:pharo-dev-boun...@lists.pharo.org] On Behalf Of
> Christophe Demarey
> Sent: Thursday, December 1, 2016 11:49 AM
> To: Pharo Development List <firstname.lastname@example.org>
> Subject: [Pharo-dev] Set internal array size
> I just discovered a funny thing.
> If you create a Set with Set new, you will get a Set with an internal array
> of 5 elements (hardcoded in Set class>>#new).
> If you ask explicitly a Set for one or no element: Set new: 0 (or a number
> between 0 and 5), you will get an internal array of 7 elements.
> This behavior is a bit strange. Either we always need at least 7 elements and
> we need to update Set class>>#new, either the method Set class>>#sizeFor:
> should be updated.