Groups > comp.lang.java.programmer > #26610

Re: can this be done with generics?

From	Mike Amling <mamling@chaff.us>
Newsgroups	comp.lang.java.programmer
Subject	Re: can this be done with generics?
Date	2013-11-25 09:02 -0600
Message-ID	<bfh72pFqrh7U1@mid.individual.net> (permalink)
References	<slrnl9580s.42s.avl@gamma.logic.tuwien.ac.at>

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On 11/24/13 6:55 PM, Andreas Leitgeb wrote:
> I'd like to use the "call methods in a chain" pattern
> across a class-subhierarchy, with most of the methods
> defined in the base-class.
>
> Suppose, I had two classes:
>
>   class Foo {
>      public Foo foo1() {
>         /* do something very interesting ... */
>         return this;
>      }
>      // assume there were like 100 such foo#() methods here
>      //  (in practice they of course have more diverse names)
>   }
>   class Bar extends Foo {
>      public Bar bar() {
>         /* do something very interesting */
>         return this;
>      }
>   }
>
> And then, somewhere else:
>
>    // the single-class chain works just fine:
>    new Foo().foo1().foo42().foo84();
>
>    // but if I start with a Bar, and eventually after some foo#() calls
>    // want to call method bar() which is not in Foo, then I'm out of luck:
>    new Bar().foo1().foo42().foo84().bar(); // doesn't work, of course!
>
> Is there a way to use *generics* for the methods of class Foo such that
> each foo#() returns the *static* type on which the compiler saw it
> applied?
>
> Alternatives, that do NOT satisfy me:
>    a) use an explicit cast to (Bar)
>        ((Bar)(new Bar().foo1().foo42().foo84())).bar();
>       Would turn into a nightmare, when more of Bar's
>       methods got mixed into the chain.
>...
> I'm pretty sure, that this would be principally possible (as in: the
> compiler has all the information that would be needed),

I don't think the compiler has all the information needed to guarantee 
that new Bar().foo1().bar() will be executable at runtime. The compiler 
may know, from the "return this" in foo1 that it's safe if you run with 
the Foo.class and the Bar.class files that it is now generating. But the 
compiler also should know that the Bar.class file it's writing may be 
run with a Foo.class file from a later compile of a Foo.java that's been 
changed to, say,

public Foo foo1() {
   // Wonderful things
   return new Foo();
}

Mike Amling
--
Silvio, Silvio grande

Thread

can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-25 00:55 +0000
  Re: can this be done with generics? Arne Vajhøj <arne@vajhoej.dk> - 2013-11-24 21:11 -0500
    Re: can this be done with generics? Saxo <jeti789@web.de> - 2013-11-25 01:43 -0800
      Re: can this be done with generics? Saxo <jeti789@web.de> - 2013-11-25 01:47 -0800
      Re: can this be done with generics? Arne Vajhøj <arne@vajhoej.dk> - 2013-11-26 21:32 -0500
    Re: can this be done with generics? Silvio <silvio@internet.com> - 2013-11-25 11:30 +0100
      Re: can this be done with generics? Saxo <jeti789@web.de> - 2013-11-25 02:36 -0800
      Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-25 10:45 +0000
      Re: can this be done with generics? Arne Vajhøj <arne@vajhoej.dk> - 2013-11-26 21:35 -0500
        Re: can this be done with generics? Silvio <silvio@internet.com> - 2013-11-27 10:48 +0100
        Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-27 10:18 +0000
  Re: can this be done with generics? Patrick Roemer <sangamon@netcologne.de> - 2013-11-25 12:59 +0100
    Re: can this be done with generics? Robert Klemme <shortcutter@googlemail.com> - 2013-11-25 22:31 +0100
      Re: can this be done with generics? Patrick Roemer <sangamon@netcologne.de> - 2013-11-26 12:03 +0100
      Re: can this be done with generics? v_borchert@despammed.com (Volker Borchert) - 2013-11-26 21:32 +0000
        Re: can this be done with generics? Robert Klemme <shortcutter@googlemail.com> - 2013-11-26 23:30 +0100
      Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-27 18:53 +0000
        Re: can this be done with generics? Sebastian <news@seyweiler.dyndns.org> - 2013-11-28 22:28 +0100
          Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-30 14:21 +0000
  Re: can this be done with generics? Mike Amling <mamling@chaff.us> - 2013-11-25 09:02 -0600
    Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-26 01:04 +0000
      Re: can this be done with generics? Robert Klemme <shortcutter@googlemail.com> - 2013-11-26 08:16 +0100
        Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-26 20:42 +0000
    Re: can this be done with generics? Arne Vajhøj <arne@vajhoej.dk> - 2013-11-26 21:38 -0500
      Re: can this be done with generics? Mike Amling <mamling@chaff.us> - 2013-11-27 11:05 -0600
  Re: can this be done with generics? taqmcg@gmail.com - 2013-11-25 08:36 -0800
    Re: can this be done with generics? taqmcg@gmail.com - 2013-11-25 09:04 -0800
      Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-26 00:50 +0000
        Re: can this be done with generics? Arivald <NOSPAMarivald@interia.pl> - 2013-11-26 07:10 +0100
          Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-11-27 18:58 +0000
  Re: can this be done with generics? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-12-07 09:04 -0800
    Re: can this be done with generics? Andreas Leitgeb <avl@gamma.logic.tuwien.ac.at> - 2013-12-07 19:20 +0000
      Re: can this be done with generics? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2013-12-10 11:14 -0800

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