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