switch

[Steven D'Aprano]

On Wed, 09 Dec 2009 18:50:29 +0000, Nobody wrote:

> On Tue, 08 Dec 2009 21:02:44 -0800, Kee Nethery wrote:
> 
>> I string together a bunch of elif statements to simulate a switch
>> 
>> if foo == True:
>> 	blah
>> elif bar == True:
>> 	blah blah
>> elif bar == False:
>> 	blarg
>> elif ....
> 
> This isn't what would normally be considered a switch (i.e. what C
> considers a switch). 

Anyone would think that C was the only programming language in 
existence...


> A switch tests the value of an expression against a
> set of constants.

In C. Things may be different in other languages.

For example, I recall the so-called "4GL" (remember when that was the 
marketing term of choice for interpreted programming languages?) 
Hyperscript from Informix. I can't check the exact syntax right now, but 
it had a switch statement which allowed you to do either C-like tests 
against a single expression, or if-like multiple independent tests.

Moving away from obsolete languages, we have Ruby which does much the 
same thing: if you provide a test value, the case expression does a C-
like test against that expression, and if you don't, it does if-like 
multiple tests.

http://www.skorks.com/2009/08/how-a-ruby-case-statement-works-and-what-
you-can-do-with-it/



> If you were writing the above in C, you would need to
> use a chain of if/else statements; you couldn't use a switch.
> 
> Compiled languages' switch statements typically require constant labels
> as this enables various optimisations.

Pascal, for example, can test against either single values, enumerated 
values, or a range of values:

case n of
   0:
     writeln('zero');
   1, 2:
     writeln('one or two');
   3...10:
     writeln('something between three and ten'); 
   else writeln('something different'); 
 end;



-- 
Steven