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Date: 8 Apr 93 22:28:25 GMT
From: alex@MIMSY.CS.UMD.EDU  (Alex Blakemore)
Subject: Re: and then
Message-ID: <66217@mimsy.umd.edu>
List-Id: <comp.lang.ada>

jnestoriak@vnet.IBM.COM writes:
>> At a recent code inspection, someone suggested that I convert a
>> series of and's to and then's "for performance".  

firth@sei.cmu.edu (Robert Firth) writes:
> Don't do it.  The short-circuit forms "and then" and "or else" are
> there to allow you to state that the two conditions must be tested
> in the order in which they are written ...
> where the code would be incorrect with just "and".  

for the most part, I agree, but you should consider the case
where one branch is much more expensive than the other to compute
and its in a tight loop, frequently called primitive or other
time critical situation.

a frequent candidate is a condition combining a boolean variable or simple
expression with a complex function call.  then it may well be worth
the short circuit operator.

  if boolean_variable and then complex_function (.. lots of expensive args) the
n

you cant rely on compiler optimizations to get the same effect unfortunately
since the function must be called in case it raises an exception
to maintain portablility (I believe).
-- 
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Alex Blakemore alex@cs.umd.edu   NeXT mail accepted