Path: utzoo!attcan!uunet!mcvax!ukc!warwick!rlvd!cmc
From: cmc@inf.rl.ac.uk (Chris Crampton)
Newsgroups: comp.lang.c++
Subject: Re: Smalltalk-80 like inheritance in C++ possible ?
Message-ID: <5481@rlvd.UUCP>
Date: 16 Mar 89 13:40:46 GMT
References: <110@honold.UUCP>
Reply-To: cmc@inf.rl.ac.uk (Chris Crampton)
Organization: Rutherford Appleton Laboratory, Didcot. UK.
Lines: 105

In article <110@honold.UUCP> franco@honold.UUCP (Franco Monti) writes:
>    How can I translate the behavior of
>    the code outline [below] to the appropiate structures in C++ ?
>    ...
>
>    class name       One
>    superclass       Object
>    instance methods 
>
>	test
>	    ^1     
>        
>	result1
>	    ^self test
>

	class One
	 {
	public:
		virtual int	test()		{ return 1;		}
		int		result1()	{ return test();	}
	 };

	// The "virtual" function is the key to what you are after.
	// Strictly speaking, the class could be a struct as there
	// are no private or protected declarations
>
>    class name       Two
>    superclass       One
>    instance methods 
>
>	test
>	    ^2     

	class Two : public One
	 {
	public:
		int	test()		{ return 2;	}
	 };
>
>    class name       Three
>    superclass       Two
>    instance methods 
>
>	result2
>	    ^self  result1
>	result3
>	    ^super test
>

	class Three : public Two
	 {
	public:
		int	result2()	{ return result1();	}
		int	result3()	{ return Two::test();	}
	 };

	// I am not quite sure how significant the "^super" is
	// in your example.  Depending what you want, the "Two::"
	// may not be necessary.
>
>   (*************************************)
>
>   Now create new instances:
> 
>    example1 <- One new
>    example2 <- Two new
>    example3 <- Three new

	One	example1;
	Two	example2;
	Three	example3;
>
>    and consider scenarios like this:
>
>    expression           result
>    ----------           ------
>
>    example1 test          1
>    example1 result1       1 
>    example2 test          2 
>    example2 result1       2 
>    example3 test          2 
>    example3 result2       2 
>    example3 result3       2

     example1.test()        1
     example1.result1()     1
     example2.test()        2
     example2.result1()     2
     example3.test()        2
     example3.result2()     2
     example3.result3()     2

Hope this answers your question.

Chris.

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Chris M Crampton		JANET:	cmc@uk.ac.rl.inf
Informatics Department		ARPA:	cmc%inf.rl.ac.uk@nss.cs.ucl.ac.uk
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