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From: ali@navajo.UUCP
Newsgroups: comp.lang.pascal
Subject: Re: Help on conformant arrays wanted...
Message-ID: <1402@navajo.STANFORD.EDU>
Date: Sat, 21-Feb-87 21:45:24 EST
Article-I.D.: navajo.1402
Posted: Sat Feb 21 21:45:24 1987
Date-Received: Mon, 23-Feb-87 05:46:44 EST
References: <1040@gould9.UUCP>
Reply-To: ali@navajo.UUCP (Ali Ozer)
Organization: Stanford University
Lines: 48

In article <1040@gould9.UUCP> joel@gould9.UUCP (Joel West) writes:
>...The closest I could come is that a conformant array is a parameter 
>in which the type of the element is fixed, but the upper and lower
>bounds are implicit parameters.
> Joel West

Conformant arrays provide a way with which procedures do not have to know
about the size of the array they are getting. Consider the following
declaration:

function StrLen (s: packed array [lo..hi: integer] of char): integer;

StrLen expects to receive a packed array of characters, indexed by integers.
Thus all of the following are legal calls:

var s1: packed array [1..6] of char;
    
n := StrLen (s1);   
n := StrLen ('foo');
n := StrLen ('');

When you call StrLen with s1, s will become a packed array of 6 characters,
and lo will be set to 1, and hi will be set to 6. When you call StrLen
with 'foo', s will become 'foo' and lo and hi will be 1 and 3, respectively.
In the last case, lo will be 1 and hi will be 0.

Note that conformant arrays are most useful with packed arrays of characters.
(And that's why my 3 examples include them...). Also note that when you
pass in a constant string (ie, a literal), the lower bound automatically
gets 1 --- This is a special case (as in no other instance can you pass in
a constant array).

Another example of conformant arrays could be:

procedure ClearCharCount (var foo : array [low..high: char] of integer);
var ch : char;
begin
  for ch := low to high do foo[ch] := 0;
end;

Then you could call the above procedure with all of the following arrays:

var lowercase: array ['a'..'z'] of integer;
    uppercase: array ['A'..'Z'] of integer;
    all      : array [' '..'~'] of integer;


Ali Ozer, ali@navajo.stanford.edu