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From: shang@corp.mot.com (David L. Shang)
Subject: Re: Eiffel and Java
Date: 1996/11/04
Message-ID: <1996Nov4.140227.4601@schbbs.mot.com>#1/1
X-Deja-AN: 194501325
sender: news@schbbs.mot.com (SCHBBS News Account)
references: <55ditr$pnh@gaia.ns.utk.edu>
organization: MOTOROLA 
reply-to: shang@corp.mot.com
newsgroups: 
 comp.lang.eiffel,comp.lang.ada,comp.lang.sather,comp.lang.java.advocacy,comp.object
Date: 1996-11-04T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <55ditr$pnh@gaia.ns.utk.edu> mbk@caffeine.engr.utk.edu (Matt Kennel)  
writes:
> David L. Shang (shang@corp.mot.com) wrote:
> : But Sather's superclass construction is limited to non-parametrerized
> : classes only.
> 
> This isn't true, at least in 1.1.  The following compiles and executes. 
> 
> -------------------------------------------------------
> -- demonstrate abstract superclass over a parameterized type. 
> -------------------------------------------------------
> abstract class $OVER{T} > $P{T} is
>    feature1(arg:T);
> end;
> 
> abstract class $P{T} is
>   feature1(arg:T);
>   feature2(arg:T);
> end; 
> 
> class CONCRETE{T} < $OVER{T} is
>    feature1(arg:T) is #OUT + "In feature\n"; end;
>    create:SAME is return new; end; 
> end;    
> 
>    
> class MAIN is
> 	main is
> 	  #OUT + "Hello World.\n";
> 	  
> 	  ob :$OVER{INT} := #CONCRETE{INT}; 
> 	  ob.feature1(42);
> 
>         end;
> end;
> 

Try the following, if Sather's compiler does not complain, then,
Sather's generic class is equivalent to Transframe's:

class MAIN is
	main is
	  #OUT + "Hello World.\n";
	  
	  ob :$OVER;
	  if (some_input_condition) ob := #CONCRETE{INT}; 
	  else ob = #P(STRING);
	  
	  // at this point, we don't know the exact element type of ob
	  // type assurance must be used
	  assume (typeof(ob).ElementType is INT) ob.feature1(42);

        end;


> : Transframe provides a more powerful superclass construction that 
> : can support parameterized classes.
> 
> : Suppose we have two existing classes
> : ....
> 
> I believe that Sather could express the same concept. 
> 

The concept of generic class in Sather is different than Transframe's.

David Shang