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From: franka@mmintl.UUCP (Frank Adams)
Newsgroups: comp.lang.c++
Subject: Re: virtual constructors
Message-ID: <2435@mmintl.UUCP>
Date: Tue, 29-Sep-87 17:09:52 EDT
Article-I.D.: mmintl.2435
Posted: Tue Sep 29 17:09:52 1987
Date-Received: Mon, 5-Oct-87 08:21:57 EDT
References: <895@saturn.ucsc.edu>
Reply-To: franka@mmintl.UUCP (Frank Adams)
Organization: Multimate International, E. Hartford, CT.
Lines: 28
Keywords: constructors, derived

In article <895@saturn.ucsc.edu> conrad@jupiter.ucsc.edu (Al Conrad) writes:
>Virtual constructors are not allowed.  So if I need a a copy
>of a particular object which has derived classes, how do I
>do it?  For example: rectangle, circle, line, etc. are derived
>classes of the base class *shape*.  Now I want to make a copy
>of a given shape.

class shape {
	virtual shape * copy();
}

class rectangle : public shape {
	shape * copy() {
		rectangle * answer = new rectangle;
		[copy this];
		return answer;
	}
}

If you really want a constructor, you can now add in class shape:

	shape(shape * original) {this = original->copy()};

Otherwise, you can just use the copy function.
-- 

Frank Adams                           ihnp4!philabs!pwa-b!mmintl!franka
Ashton-Tate          52 Oakland Ave North         E. Hartford, CT 06108