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.

fullLoadSet         

instVarNamed: #array put: array;

               instVarNamed: #tally put: array size.

[ fullLoadSet includes: 8; includes: Morph ] bench. "'215.157 per second'"

Best regards,

Henrik

From: Pharo-dev [mailto:pharo-dev-bounces@lists.pharo.org] On Behalf Of Christophe Demarey
Sent: Thursday, December 1, 2016 11:49 AM
To: Pharo Development List <pharo-dev@lists.pharo.org>
Subject: [Pharo-dev] Set internal array size

Hi,

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.

WDYT?

Christophe