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From: billwolf%hazel.cs.clemson.edu@hubcap.clemson.edu (William Thomas Wolfe, 2847 )
Newsgroups: comp.sw.components
Subject: Re: Assignment in Ada
Message-ID: <6556@hubcap.clemson.edu>
Date: 23 Sep 89 21:13:43 GMT
References: <TED.89Sep22225829@kythera.nmsu.edu>
Sender: news@hubcap.clemson.edu
Reply-To: billwolf%hazel.cs.clemson.edu@hubcap.clemson.edu
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From ted@nmsu.edu (Ted Dunning):
> but where does this leave ada?  no overloading or forbidding
> assignment leaves the writer of a reliable reference counting adt in a
> real pickle.

    The fact that it is not possible in Ada 83 to overload ":=" has
    not posed practical difficulties, since it is standard practice
    to simply require the generic parameter structure

       with procedure Assign (Target : in out Object_Type;
                              Source : in     Object_Type) is <>;

    thus substituting "Assign" for ":=" in a straightforward way.

    There remains a technical problem in that we can't use "Assign"
    to initialize variables at the moment of creation, which is probably
    why this is one of the more popular Ada 9X revision requests.  

    I wouldn't use either form of assignment to do a reference-counting
    system, though... it's too easy to create unkillable garbage if one
    process dies while still holding claim to a reference. 


    Bill Wolfe, wtwolfe@hubcap.clemson.edu