Generic Blues

From:

ram@zedat.fu-berlin.de (Stefan Ram)

Newsgroups:

comp.lang.java.programmer

Date:

8 Mar 2011 06:22:21 GMT

Message-ID:

<Generic-20110308062008@ram.dialup.fu-berlin.de>

  This is too messed up, nobody can help me:

[javac] de\dclj\ram\type\tuple\ComparableLocatableTuple0.java:36:
        method addrac in interface Placeable<T#2> cannot be applied to given types
[javac] components[ position ].addrac( this, position ); }
[javac] ^
[javac] required: Comparable<T#1>,int
[javac] found: ComparableLocatableTuple0<T#1>,int
[javac] where T#1,T#2 are type-variables:
[javac] T#1 extends Comparable<T#1>,Locatable<T#1> declared in class ComparableLocatableTuple0
[javac] T#2 extends Object declared in interface Placeable

  I want this line to compile. If you somehow already know,
  what I need to do now, please let me know. Otherwise, I try
  to provide more details:

  The type of ?components[ position ]? is T (in this scope),
  which is given as:

< T extends java.lang.Comparable< T >& de.dclj.ram.system.locator.Locatable< T >>

  The type of ?this? is ComparableLocatableTuple0:

package de.dclj.ram.type.tuple;
public class ComparableLocatableTuple0
< T extends java.lang.Comparable< T >& de.dclj.ram.system.locator.Locatable< T >>
implements de.dclj.ram.type.tuple.ComparableLocatableTuple< T >
{ ... }

  More about some types used or mentioned:

package de.dclj.ram.system.locator;
public interface Locatable< T >
extends
de.dclj.ram.system.locator.Findable,
de.dclj.ram.system.locator.Placeable< T >{}

package de.dclj.ram.type.tuple;
public interface ComparableLocatableTuple< T >
extends de.dclj.ram.type.tuple.ComparableTuple< T >,
de.dclj.ram.system.locator.Locatable< T >{}

package de.dclj.ram.type.tuple;
public interface ComparableTuple< T extends java.lang.Comparable< T >>
extends java.lang.Comparable<de.dclj.ram.type.tuple.ComparableTuple< T >>,
de.dclj.ram.type.tuple.Tuple

package de.dclj.ram.system.locator;
public interface Placeable< T >
{ void addrac( java.lang.Comparable< T >container, int position ); }

  (Please let me know, what else you need to do.
  Should I try to extract a SSCCE from my project?)

  So, ?this? is of a subtype of

java.lang.Comparable<de.dclj.ram.type.tuple.ComparableTuple< T >>

  and the compiler wants

Comparable<T#1>

  ? The compiler cannot unify the type ?T#1? with
  de.dclj.ram.type.tuple.ComparableTuple< T >?
  Possibly, due to different bounds for these T?

  But the type of ?this? actually extends

de.dclj.ram.type.tuple.ComparableTuple< T >

  ! (Albeit possibly with ?T? being in another scope and
  thus having another meaning.)

  I feel as if I am not smart enough for this stuff. Or I was
  too much in a rush to add type parameters everywhere, so
  that I did not properly document what my type parameters
  actually are intended to convey.

  The compiler is Java 1.7, version 7.0.0.107.

<javac
  source='1.7'
  target='1.7'
  deprecation='on'
  debug='on'
  optimize='off'
  >
  <compilerarg line='-Xlint '/>
  <compilerarg line='-Xlint:-unchecked '/>
  <compilerarg line='-Xlint:-serial '/>
  <compilerarg line='-Xmaxerrs 1 -Xmaxwarns 2147483647'/>
  </javac>