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Path: utzoo!utgpu!watmath!clyde!att!rutgers!mailrus!ukma!gatech!linus!mbunix!eachus
From: eachus@mitre-bedford.ARPA (Robert Eachus)
Newsgroups: comp.lang.ada
Subject: Re: Collective response to := messages
Summary: Basic operations are overloaded!!
Keywords: User defined assignment
Message-ID: <42334@linus.UUCP>
Date: 30 Nov 88 18:24:27 GMT
References: <8811282217.AA04896@ajpo.sei.cmu.edu> <24856@sri-unix.SRI.COM>
Sender: news@linus.UUCP
Reply-To: eachus@mbunix.mitre.org (Robert I. Eachus)
Organization: The MITRE Corporation, Bedford, Mass.
List-Id: <comp.lang.ada>


     There has been a lot of frothing at the mouth on both sides of
this issue about what is or is not the Ada model of assignment.  First
of all a lot has been said about what a change to the language it
would be to make assignment or other basic operations overloadable.
However, if you look in 8.7 Context of Overload Resolution, the first
paragraph states:

     "Overloading is defined for subprograms, enumeration literals,
operators, and single entries, and also for the operations that are
inherent in several basic operations such as assignment, membership
tests, allocators, the literal null, aggregates, and string literals."

      Overloading, and overload resolution involving basic operations
is a fact of Ada life.  If you think otherwise try:

      package Overload_Test is
        type A is access Boolean;
        B: constant Boolean := null = null;
        type C is access Character;
        D: constant Boolean := null = null;
      end Overload_Test;

      The compiler should accept the decalartion of B, but reject the
declaration of D.  A lot of work went on during the language
definition process to make similar (but useful) cases work for numeric
types. If you object that this example involves equality which is not
a basic operation instead try:

       package Overload_Two is
	 A: Boolean := 'b' in 'a'..'c';
         type New_Char is ('b', 'a', 'c');
	 C: Boolean := 'b' in 'a'..'c';
       end Overload_Two;