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From: Hyman Rosen <hymie@prolifics.com>
Subject: Re: Ada OO Mechanism
Date: 1999/06/03
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Date: 1999-06-03T16:48:31+00:00
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Matthew Heaney <matthew_heaney@acm.org> writes:
>   type Human_Type (<>) is tagged limited private;
>   procedure Marry (Bride, Groom : in out Human_Type);
> This is a binary operation:
>   Marry (Linda, Paul);
> The operation applies equally to both parties, so designating one object
> as the distinguished receiver would not capture the abstraction as well.

I see. I think at this point, C++ programmers would have to code the
tag test themselves, but then the usage would look very similar.

struct Human_Type
{
        friend Marry(Human_Type &a, Human_Type &b)
        {
                if (typeid(a) != typeid(b))
                        throw "Marriage of unequals!";
                a.Marry(b);
        }
private:
	virtual void Marry(Human_Type &other) = 0;
};

struct Lord : Human_Type
{
private:
	virtual void Marry(Human_Type &other)
	{
                Lord &other_lord = static_cast<Lord &>(other);
                //...
	}
};