Implementing #at:ifPresent:ifAbsentPut: without reusing #at:ifAbsent: and 
#at:ifAbsentPut: implies that it must be defined in some of its subclasses 
too to make it work.
This is the reason why #at:ifAbsentPut: and #at:ifPresent:ifAbsent: reuse 
the low-level methods, sacrificing performance.

Levente

On Fri, 25 Sep 2015, commits at source.squeak.org wrote:

> Eliot Miranda uploaded a new version of Collections to project The Trunk:
> http://source.squeak.org/trunk/Collections-eem.656.mcz
>
> ==================== Summary ====================
>
> Name: Collections-eem.656
> Author: eem
> Time: 25 September 2015, 11:36:48.911 am
> UUID: 50ec1b3e-c058-4167-889e-836e994b500b
> Ancestors: Collections-ul.655
>
> Add Dictionary>>at:ifPresent:ifAbsentPut:.
> Move Dictionary>>fasterKeys & keyForIdentity: to 50Deprecated
>
> =============== Diff against Collections-ul.655 ===============
>
> Item was added:
> + ----- Method: Dictionary>>at:ifPresent:ifAbsentPut: (in category 'accessing') -----
> + at: key ifPresent: oneArgBlock ifAbsentPut: absentBlock
> + 	"Lookup the given key in the receiver. If it is present, answer the value of
> + 	 evaluating oneArgBlock with the value associated with the key. Otherwise
> + 	 add the value of absentBlock under the key, and answer that value."
> +
> + 	| index value |
> + 	index := self scanFor: key.
> + 	(array at: index) ifNotNil:
> + 		[:element|
> + 		 ^oneArgBlock value: element value].
> + 	value := absentBlock value.
> + 	self atNewIndex: index put: (Association key: key value: value).
> + 	^value!
>
> Item was removed:
> - ----- Method: Dictionary>>fasterKeys (in category 'accessing') -----
> - fasterKeys
> - 	"Contrary to old version of #keys, this method returned an Array rather than a Set.
> - 	This was faster because no lookup: was performed.
> - 	But now, #keys also return an Array, so don't use #fasterKeys anymore."
> -
> - 	self deprecated: 'use #keys'.
> -
> - 	^self keys.
> - !
>
> Item was removed:
> - ----- Method: Dictionary>>keyForIdentity: (in category 'accessing') -----
> - keyForIdentity: anObject
> - 	"If anObject is one of the values of the receive, return its key, else return nil.  Contrast #keyAtValue: in which there is only an equality check, here there is an identity check"
> -
> - 	self deprecated: 'Use #keyAtIdentityValue:ifAbsent:'.
> - 	^self keyAtIdentityValue: anObject ifAbsent: nil!
>
>
>