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From: andrewd@cs.adelaide.edu.au (Andrew Dunstan)
Newsgroups: comp.lang.ada
Subject: Re: generic queue packages
Message-ID: <1mp0h3INNp2u@huon.itd.adelaide.edu.au>
Date: 28 Feb 93 00:20:51 GMT
References: <1993Feb24.212641.8326@evb.com>
 <1993Feb26.031650.3447@leeweyr.sccsi.com>
 <1993Feb26.190255.24811@seas.gwu.edu>
Organization: The University of Adelaide
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Date: 1993-02-28T00:20:51+00:00
List-Id: <comp.lang.ada>

In article <1993Feb26.190255.24811@seas.gwu.edu>, mfeldman@seas.gwu.edu (Michael Feldman) writes:

[he dislikes]
|> TYPE Stupid (Length: Positive := 8) IS RECORD
|>   String_Part: String(1..Length);
|> END RECORD;
|> 
[he prefers]
|> 
|> SUBTYPE Realistic IS Integer RANGE 1..64; -- for example
|> TYPE Smart (Length: Realistic := 8) IS RECORD
|>   String_Part: String(1..Length);
|> END RECORD;
|> 
|> will waste at most 64 characters' worth, whether the compiler chooses
|> static or dynamic allocation. That's a whole lot better than the
|> roughly 2 gigabytes you'd try to allocate for a record of the first
|> type, if the compiler used static allocation and Integer was 32 bits.
|> (TeleSoft and Verdix do this, for example.) So it's (more) portable.
|> 
|> Variant records are a GREAT way to test intelligent design decisions.
|> Don't blame bad ones on the language or the compiler, friends.
|> 
|> Mike Feldman


A "realistic" maximum might still be quite large. Say we allow lines up
to 255 chrs. Storage of 100,000 lines of average length 10 will still 
waste megabytes of memory if a static allocation strategy is used by the 
compiler.

That is why I generally avoid this sort of use of variant records for
this sort of processing - if I want dynamic sizing I make it explicit
by doing it myself - that makes for portable code. It also means I
don't have to use arbitrary limits on the size of some structure.


-- 
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#  Andrew Dunstan (formerly of the) #   There's nothing good or bad   #
#  Department of Computer Science   #   but thinking makes it so.     #
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