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Change Lift to use rx.Observable.Operator #857

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merged 1 commit into from
Feb 12, 2014

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benjchristensen
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The generics insanity has to stop.

This pull request is a result of @abersnaze and I continuing to fail to make generics work with this signature:

Func1<Subscriber<? super R>, Subscriber<? super T>>

It all fell apart while trying to do things that needed the equivalent of:

Func1<Subscriber<? super R>, Subscriber<? super ? super T>>

... and other such variants.

With this change I can also finally get the OperatorMerge generics to work.

Thus, the Operator type exists inside Observable just like OnSubscribe like this:

    /**
     * Operator function for lifting into an Observable.
     */
    public interface Operator<R, T> extends Func1<Subscriber<? super R>, Subscriber<? super T>> {
        // cover for generics insanity
    }

This gives us imports like this:

import rx.Observable;
import rx.Observable.OnSubscribe;
import rx.Observable.Operator;

I know it's not as pure as having lift(Func1) but this is far more usable.

public <R> Observable<R> lift(final Operator<R, T> bind)

If anyone has a different suggestion that still solves the generics issue please let me know.

The generics insanity has to stop.
@benjchristensen
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If you doubt the insanity, here's an error message for the merge operator :-)

The method lift(Func1<Subscriber<? super R>,Subscriber<? super capture#210-of ? extends Observable<? extends T>>>) in the type Observable<capture#210-of ? extends Observable<? extends T>> is not applicable for the arguments (OperatorMerge)

@benjchristensen
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Apparently only the IDE likes merge now ... curse generics.

/Users/bechristensen/development/github/RxJavaFork/rxjava-core/src/main/java/rx/Observable.java:1780: error: method lift in class Observable<T#1> cannot be applied to given types;
        return source.lift(new OperatorMerge<T>());
                     ^
  required: Operator<R,CAP#1>
  found: OperatorMerge<T#2>
  reason: no instance(s) of type variable(s) R exist so that argument type OperatorMerge<T#2> conforms to formal parameter type Operator<R,CAP#1>
  where R,T#1,T#2 are type-variables:
    R extends Object declared in method <R>lift(Operator<R,T#1>)
    T#1 extends Object declared in class Observable
    T#2 extends Object declared in method <T#2>merge(Observable<? extends Observable<? extends T#2>>)
  where CAP#1 is a fresh type-variable:
    CAP#1 extends Observable<? extends T#2> from capture of ? extends Observable<? extends T#2>

benjchristensen added a commit that referenced this pull request Feb 12, 2014
Change Lift to use rx.Observable.Operator
@benjchristensen benjchristensen merged commit 55a7984 into ReactiveX:master Feb 12, 2014
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@benjchristensen
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After fixing generics, it actually would be:

public <R> Observable<R> lift(final Func1<? extends Subscriber<? super R>, ? super Subscriber<? super T>> bind)

Using the Operator type it is instead:

public <R> Observable<R> lift(final Operator<? extends R, ? super T> bind)

as the type gives cover for:

public interface Operator<R, T> extends Func1<Subscriber<? super R>, Subscriber<? super T>>

@benjchristensen benjchristensen deleted the operator-type branch February 12, 2014 17:39
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2 participants