The code of Pharo for + **may** be rewritten using double dispatch but it is not that clear to me especially the adaptToInteger logic and we do not change for the sake of it :) There are plenty of places we should improve and that are really important.
In Pillar, or compiler we have many more nodes and there a Visitor is clearly the way to go. Now you should try and sketch something and let us know. There is not need to create a superclass between die and dieHandle because DD is not based on nominal subtyping. We just need objects proposing the correct API. I use abstract superclass when I want to really push on contract or interfaces. Now in this book I did not want to stress inheritance. So I wanted to have a solution stressing messages because often people forget that messages and polymorphism are powerful and not systematically linked with inheritance. Stef On Tue, Aug 29, 2017 at 6:47 PM, Yves Lenfant <lenfan...@wanadoo.fr> wrote: > Ooops I wasn't int the mailing list, lets try again > > Hello Steph, > > I have questions about the concept because,probably, I miss something. > I am not sneaky, let me explain. > > If we analyse the Kernel Numbers package, and we dissect the relation > between Float, Fraction and Integer (Pharo 5.0) for example, the '+' method > in the class Integer. We read: > > + aNumber > "Refer to the comment in Number + " > > aNumber isInteger > ifTrue: [ self negative == aNumber negative > ifTrue: [ ^ (self digitAdd: aNumber) > normalize ] > ifFalse: [ ^ self digitSubtract: aNumber ] > ]. > aNumber isFraction > ifTrue: [ ^ Fraction > numerator: self * aNumber denominator + > aNumber numerator > denominator: aNumber denominator ]. > ^ aNumber adaptToInteger: self andSend: #+ > > and we have similar '+'method containing complementary tests in the other > class Float and Fraction. > And an overall '+' method in the class Number > > + aNumber > "Answer the sum of the receiver and aNumber." > > self subclassResponsibility > > > I precise that a long time ago as an academic exercice, I developped a > 'Complex' class using this way above (So I add tests). > > My questions: > You say it's better to use double dispatch, so in this case, can we apply it > for the Number subclasses? > > It is good or unnecesary to create a super class 'Dicable' containing a '+' > method with > > + aNumber > "Answer the sum of the receiver and aNumber." > > self subclassResponsibility > > ? is it wasted time or safe code? > > Yves > > > > -- > View this message in context: > http://forum.world.st/new-chapter-on-double-dispatch-for-new-book-tp4963645p4965495.html > Sent from the Pharo Smalltalk Users mailing list archive at Nabble.com. >
