It would really REALLY **REALLY** help if we knew what the heck you were trying to do. There is an excellent chance that it is MUCH simpler than you think. If you cannot show us the Smalltalk version of the problem, can you show us the version for some other language?
On Sun, 7 Apr 2019 at 20:15, Roelof Wobben <r.wob...@home.nl> wrote: > Op 6-4-2019 om 15:15 schreef K K Subbu: > > On 06/04/19 4:49 PM, Roelof Wobben wrote: > >> Hello, > >> > >> I just learned double dispatch. > >> And now for the Robot challenge of exercism Tim has pointed me to > >> this > >> article( > https://blog.metaobject.com/2019/04/accessors-have-message-obsession.html) > > >> > >> but I fail to see how the move method looks like in that article. > >> I had a conversation with Tim in the exercism channel and the way he > >> explains it, it looks like double dispatch for me. > >> > >> Am I on the right track or do I oversee something here. > > unary methods like moveRight perform specific ops and are not > > parametric, so only a single dispatch, depending on the receiver, is > > needed. > > > > If you change it to move: aDistanceOrAngle, then performing requests > > like "move: 3 cms" or "move: 30 degrees" will depend not only on the > > receiver but also on the class of the argument. This would need double > > dispatch (aka multiple polymorphism). The first dispatch would be > > based on the receiver and the receiver's method would then dispatch it > > based on the class of the argument (i.e. Distance>>move or Angle>>move ) > > > > HTH .. Subbu > > > > > > > hmm, still stuck > > I have now a class Direction with as instance variables north, south, > east, west > and made the accessors. > > then I thought I need a initialize like this : > > initialize > north = Direction( 0, -1). > east = Direction( 1, 0). > south = Direction( 0, 1). > west = Direction(-1, 0). > > but the Direction (0,-1) is a problem . the compiler does not like the > (0,-1) part > > to give you the big picture. I have a Robot which can turnRight , > turnLeft and moveForward and I try to understand how the page would work > in my case. > > So I have a object Direction as described above and a Object MoveForward > which is a subobject of Direction. > MoveForward has only 1 method : > > IsMove > ^ 'A' > > Roelof > > >
