Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!orion.oac.uci.edu!ucivax!milne
From: milne@ics.uci.edu (Alastair Milne)
Newsgroups: comp.lang.pascal
Subject: Re: case (string) of
Message-ID: <285076CC.12795@ics.uci.edu>
Date: 8 Jun 91 06:18:52 GMT
References: <1991Jun3.222059.16125@javelin.sim.es.com> <1048.284bd1ff@vger.nsu.edu>
Distribution: na
Organization: UC Irvine Department of ICS
Lines: 38

In <1048.284bd1ff@vger.nsu.edu> g_harrison@vger.nsu.edu (George C. Harrison, Norfolk State University) writes:

>In article <1991Jun3.222059.16125@javelin.sim.es.com>, tpehrson@javelin.sim.es.com (Tim Clinkenpeel) writes:
>> so i can't use case for strings, eh?  what are my alternatives?  a list of
>> if-thens?  (tp5.0)

>A list of if-then's in not so bad if you structure them correctly.  After all
>isn't that what case is all about?  

   Often not.  Turbo may implement them this way -- it's stepping during
   debugging seems to say so -- but jump tables are a preferred way
   if their size for the indexes of the give table is not prohibitive.
   A clever compiler will use an optimal mix of conditional jumps 
   and jump tables.

>As an alternative you may want to convert
>the string or part thereof to an enumerated type and use a variable of that
>type in the case statement; however, in general, this does not allow for
>string's that don't conform to the type.

   As in ...

   ** a hash function **

   The good part is it can be pretty quick conversion, depending on
   what function you use, and it frees you from playing games with
   the lengths of the strings you will be using.

   The bad part is you have to deal with hash collisions, either by 
   using a function specialised to the set of strings you know you
   will have, or by more iterative hash resolution techniques.
   A full hash table is probably a good idea.  If you record, with each
   string you're prepared to recognise, an enumeration that identifies 
   it, it becomes very easy just to return the enumerated value (including
   one for "none", of course) and index the case on that.


   Alastair Milne