Path: utzoo!mnetor!uunet!mcvax!ukc!its63b!aiva!richard
From: richard@aiva.ed.ac.uk (Richard Tobin)
Newsgroups: comp.lang.c
Subject: Re: The D Programming Language: switches
Message-ID: <298@aiva.ed.ac.uk>
Date: 22 Mar 88 23:05:25 GMT
References: <222965b9@ralf.home> <941@micomvax.UUCP> <3074@haddock.ISC.COM> <25835@cca.CCA.COM>
Reply-To: richard@uk.ac.ed.aiva (Richard Tobin)
Organization: Bannerman's Bar, Cowgate, Edinburgh
Lines: 19

In article <25835@cca.CCA.COM> g-rh@CCA.CCA.COM.UUCP (Richard Harter) writes:
>	Theoretically the switch construct is more powerful than an else-if
>chain because it selects in one step.  Execution is O(1) rather than O(n)
>where n is the number of branches.

No, *practically* the switch construct is more powerful because it selects
in one step.  *Theoretically* switch can compile into an if-then-else chain
(and often will, if the case values are widely separated), and an
if-then-else chain can be analysed to discover whether it can be compiled
into a jump table.

The theoretical power of a language is [determined by] the set of
algorithms it can implement.  Its efficiency in executing these algorithms
depends on its implementation, though it's obviously easier to produce
efficient implementations of some languages than others.
-- 
Richard Tobin,                         JANET: R.Tobin@uk.ac.ed             
AI Applications Institute,             ARPA:  R.Tobin%uk.ac.ed@nss.cs.ucl.ac.uk
Edinburgh University.                  UUCP:  ...!ukc!ed.ac.uk!R.Tobin