switch

[MRAB]

Steven D'Aprano wrote:
> 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;
> 
Originally the 'case' statement in Pascal didn't support ranges or a
default; they started as non-standard extensions in some
implementations. Originally, if none of the values matched then that
was a runtime error.