Yet Another Case-statement Idea
cgreuter at calum.csclub.uwaterloo.ca
Sat Jul 4 19:19:24 UTC 1998
In working on my current and perpetual Squeak project, a roguelike
game tentatively titled "The Infernal Tower", I concluded that I
could really use a case statement in order to properly handle
keyboard input. Even though there are at least two such mechanisms,
one of which works without curly brackets, I decided to be
trendy and invent my own. I present it here for your perusal:
I implemented the following method in Object:
case: obj do: block
self = obj ifTrue: [block value].
It is used as follows:
stream nextPut: 'Apple'.
stream nextPut: 'BeBox'.
stream nextPut: 'Commodore'.
...and so on...
stream nextPut: 'Zilog'.
(I realize that this example could be implemented more easily using a
Dictionary. It's just for illustration.)
-Looks like the switch/case statements we procedural
programmers know and love.
-It's very, very simple.
-It makes use of blocks and messages to do its thing, just
like the standard control structures.
-Behaviour is subtly different from what C/Pascal programmers
would expect, in that all possibilities are tried rather
than just the one that matches the receiver.
-Because of this, it's also slower. I can alleviate (sp?)
some of this by making the method return in the block, but
that's not always possible.
In addition, I've implemented #case:case:do: (but not
#case:case:case:do: or #case:case:case:case:do: yet) to simulate
simple fall-through. (#case:case:do evaluates the block if either of
its arguments equals the receiver.
I've also implemented #identityCase:do: which uses #== instead of #=
to make its comparisons, but that message is somewhat awkward.
Perhaps, I should make #case:do: use #== and implement a new method,
say #caseEq:do: which uses #=. I suspect it would also make it easier
to optimize #case:do: at compile time, should somebody want to
Now try THAT in C++!
 Currently 65% vapourware.
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