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From: macrakis@harvard.ARPA (Stavros Macrakis)
Newsgroups: net.micro,net.lang
Subject: Re: Unchecked conversion in Ada
Message-ID: <203@harvard.ARPA>
Date: Thu, 20-Jun-85 20:19:52 EDT
Article-I.D.: harvard.203
Posted: Thu Jun 20 20:19:52 1985
Date-Received: Sun, 23-Jun-85 00:47:38 EDT
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Organization: Aiken Comp. Lab., Harvard
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> > ...converts between...two types bit-to-bit; something like C's casts.

> C casts are not bit-for-bit conversions unless the conversion happens
> to be implemented as such...

I would put it differently: C casts ARE bit-for-bit conversions except
sometimes for numerical types.  To the extent that one can speak of C
having any semantics at all, this makes the semantics of C casts grossly
inconsistent.  For instance, (int) 2.3 == 2, but (*var=2.3, *((int *)
var) ) == garbage; I don't even want to begin to think about the
semantics of conversions involving unsigned's.

I also don't understand what `happens to be implemented as' means.  What
other possibilities are there for converting pointers to integers,
incompatible pointers, etc.?

So perhaps it was a bad idea to compare Unchecked_conversion in Ada to C
casts.  I just wanted to use a reference point familiar to C users.

	-s