This is cool indeed. I find an unlimited cache a bit coarse, would not really work in practice. What about
memoizedUsing: cache ^ [ :x | cache at: x ifAbsentPut: [ self value: x ] ] then you could pass in a tuned LRUCache instance, among others. Sven > On 11 Nov 2014, at 16:24, Torsten Bergmann <asta...@gmx.de> wrote: > > Phil wrote: >> thanks for the pointer. >> Now, how do I use that? > > > First: create a method BlockClosure>>#memoized in your Pharo image (see > https://gist.github.com/jcromartie/2705526) > > memoized > "returns memoized version of an unary function" > | cache | > cache := Dictionary new. > ^ [ :x | cache at: x ifAbsentPut: [ self value: x ] ]! > > > So the idea of #memoized is to return a new "outer" block who evaluates the > original block only when the computation > of the inner block was not yet done/the result of the inner evaluation is not > yet cached. > > > As you see from the comment it works for "unary functions" which would mean > it works > for "one argument blocks". Simple example: > > |square memo | > square:= [:x | Transcript show: 'Processing'. x * x]. > memo := square memoized. > memo value: 2. > memo value: 3. > memo value: 2. > > The Transcript only shows "Processing" two times instead of three times, so > only for the first two #value: calls > we have to calculate x * x. > > For the last evaluation on the memo block (with argument 2 again) the result > is already known from the cache, > so the square block is not evaluated again. Instead the cached result could > be returned which could be faster > than doing the computation again. > > x*x is only an example - this "memoization" can usually speed up when a block > is costly (performancewise) and > is often called with the same arguments. A precondition (for this caching) is > that the block evalutes the > same way/returns the same result for the same input argument. > > > You also try the two prepared workspaces in Pharo: > > Non-memoized version: http://ws.stfx.eu/5ZE87XSFL9IH > Memoized Version: http://ws.stfx.eu/QLQLSLT7PZ4C > > Hope this makes it more clear. This simple example is a nice performance > trick and shows again the power > of Smalltalk and block closures. > > Dont know about the license - but we could ask author John Cromartie for MIT > license to include this simple > method into the standard image. I will try to contact him. > > Bye > T. >
