Groups > comp.lang.java.programmer > #8990

Re: generics puzzle

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From	blmblm@myrealbox.com <blmblm.myrealbox@gmail.com>
Newsgroups	comp.lang.java.programmer
Subject	Re: generics puzzle
Date	19 Oct 2011 13:25:46 GMT
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In article <M%hnq.3083$Oz5.1691@newsfe16.iad>,
Daniel Pitts  <newsgroup.nospam@virtualinfinity.net> wrote:
> On 10/18/11 2:45 AM, Steven Simpson wrote:
> > On 17/10/11 16:58, Daniel Pitts wrote:
> >> On 10/17/11 5:14 AM, Steven Simpson wrote:
> >>> On 17/10/11 11:41, blmblm@myrealbox.com wrote:
> >>>> One fix is to just introduce a method setFromModified() in GThing,
> >>>> but that doesn't appeal to me.
> >>>
> >>> Instead of adding it to GThing, create a static method:
> >>>
> >>> private static<T> void setModified(GThing<T> t) {
> >>> t.set(t.modified());
> >>> }
> >>
> >>
> >> What about the simpler solution:
> >>
> >> in the GThing class:
> >>
> >> public void setModified() {
> >> set(modified());
> >> }
> >
> > It "doesn't appeal" to the OP? Nor to me. Not sure I can put my finger
> > on it, but if I were the maintainer of GThing, I'd consider its
> > specification to be complete without this method. It doesn't increase
> > the value of the class as an abstraction. Adding it would certainly just
> > be a convenience for the caller. It solves a problem generated by the
> > design of the call site, not the design of the class's contract. The
> > caller can write his own routine as necessary.
> >
> Possibly, but if it is something that happens frequently, then it seems 
> more likely to belong to GThing than externally. Otherwise your 
> call-site is suffering from the code smell "feature envy"
> 
> One other approach is a "visitor" pattern:
> 

I know the "visitor" pattern (vaguely anyway), but ....  I'm not sure
I understand your version of it here, which -- does this compile?
because ....

> 
> public interface GThingVisitor {
>     <T> void visit(GThing<T> gThing);
> };

(Aside:  Hm, a generic method in an interface?!  well, why not,
maybe, but I'm not sure it would have occurred to me to try!)

> public class SetModifiedGThingVisitor {
>       <T> void visit(GThing<T> gThing) {
> 	gThing.set(gThing.modified());
>       }
> }

Was this meant to implement GThingVisitor?

> public class GThing<T> {
>     public void accept(GThingVisitor visitor) {
> 	visitor.accept(this);
>     }
> }

visitor.visit(this)??

> public class CallSite {
>     public void setAllModified(Iterable<? extends GThing<?>> things) {
>   	GThingVisitor visitor = new SetModifiedGThingVisitor();
>          for (GThing<?> thing: things) {
>              thing.accept(visitor);
>          }
>     }
> }
> 

-- 
B. L. Massingill
ObDisclaimer:  I don't speak for my employers; they return the favor.

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generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-17 10:41 +0000
  Re: generics puzzle Steven Simpson <ss@domain.invalid> - 2011-10-17 13:14 +0100
    Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-17 15:14 +0100
    Re: generics puzzle markspace <-@.> - 2011-10-17 07:33 -0700
      Re: generics puzzle Steven Simpson <ss@domain.invalid> - 2011-10-17 16:26 +0100
        Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-18 14:48 +0000
      Re: generics puzzle Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2011-10-17 15:36 +0000
    Re: generics puzzle Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-17 08:58 -0700
      Re: generics puzzle Steven Simpson <ss@domain.invalid> - 2011-10-18 10:45 +0100
        Re: generics puzzle Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-18 09:42 -0700
          Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-19 13:25 +0000
            Re: generics puzzle Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-19 10:04 -0700
              Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-20 14:14 +0000
                Re: generics puzzle Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2011-10-20 11:11 -0700
  Re: generics puzzle Robert Klemme <shortcutter@googlemail.com> - 2011-10-17 09:12 -0700
    Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-18 14:49 +0000
      Re: generics puzzle Robert Klemme <shortcutter@googlemail.com> - 2011-10-18 18:27 +0200
        Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-18 17:45 +0000
          Re: generics puzzle Robert Klemme <shortcutter@googlemail.com> - 2011-10-18 22:15 +0200
          Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-18 18:59 -0700
            Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-19 13:28 +0000
              Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-20 17:21 -0700
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-21 16:27 +0000
                Re: generics puzzle Robert Klemme <shortcutter@googlemail.com> - 2011-10-21 20:34 +0200
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-22 18:50 +0000
                Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-22 21:02 +0100
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-25 07:04 +0000
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-25 23:25 -0700
                Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-26 21:56 +0100
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-27 08:59 +0000
                eclipse shortcuts again (was Re: generics puzzle) blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-29 17:05 +0000
                Re: eclipse shortcuts again (was Re: generics puzzle) Four of Seventeen <fseventeen@gmail.com> - 2011-10-29 19:49 -0700
                Re: eclipse shortcuts again (was Re: generics puzzle) blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-31 11:17 +0000
                Re: eclipse shortcuts again (was Re: generics puzzle) Four of Seventeen <fseventeen@gmail.com> - 2011-10-31 05:39 -0700
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-23 01:30 -0700
                Re: generics puzzle Lew <lewbloch@gmail.com> - 2011-10-23 08:56 -0700
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-24 02:46 -0700
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-25 07:05 +0000
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-25 23:29 -0700
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-31 11:14 +0000
                Re: generics puzzle Four of Seventeen <fseventeen@gmail.com> - 2011-10-31 05:34 -0700
          Re: generics puzzle markspace <-@.> - 2011-10-18 21:21 -0700
            Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-19 13:29 +0000
              Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-20 17:22 -0700
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-21 16:28 +0000
              Re: generics puzzle Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-10-21 06:22 -0300
                Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-21 16:29 +0000
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-23 01:20 -0700
                Re: generics puzzle Martin Gregorie <martin@address-in-sig.invalid> - 2011-10-23 09:51 +0000
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-23 03:28 -0700
                Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-23 15:59 +0100
                Re: generics puzzle Eight of Seventeen <eights17@gmail.com> - 2011-10-24 02:46 -0700
                Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-23 15:55 +0100
            Re: generics puzzle Tom Anderson <twic@urchin.earth.li> - 2011-10-20 21:00 +0100
          Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-19 13:26 +0000
          Re: generics puzzle Arved Sandstrom <asandstrom3minus1@eastlink.ca> - 2011-10-21 05:57 -0300
            Re: generics puzzle blmblm@myrealbox.com <blmblm.myrealbox@gmail.com> - 2011-10-21 16:28 +0000

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