Re: Eiffel and Java

[mbk@caffeine.engr.utk.edu (Matt Kennel)]

David L. Shang (shang@corp.mot.com) wrote:
: 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;

I don't think the generic class concept is the same, but the following
appears to do what you desire.  The main difference is that in Sather
$TYPE{T} and $TYPE are wholly unrelated _a priori_.  $TYPE is not a superytpe
of $TYPE{T} unless explicitly declared that way, as in this example. 


---------------------
abstract class $OVER is
   -- over everything
end; 

abstract class $OVER{T} < $OVER > $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(args:ARRAY{STR}) is
      #OUT + "Hello World.\n";
	  
      ob :$OVER;
      if args[1] = "int" then
	 #OUT + "Creating int\n";
	 ob := #CONCRETE{INT}; 
      else
	 ob := #CONCRETE{STR};
      end;
      
      typecase ob
      when $OVER{INT} then ob.feature1(42);
      else #OUT + "No matching typecase\n";
      end;
   end;
end;

-------
(~/sather1/hello) caffeine.engr.utk.edu > a.out int
Hello World.
Creating int
In feature
(~/sather1/hello) caffeine.engr.utk.edu > a.out other
Hello World.
No matching typecase
(~/sather1/hello) caffeine.engr.utk.edu >
-------


: > : 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

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