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
