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1.x: distinctUntilChanged change erroneous behavior #4276

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1.x: distinctUntilChanged change erroneous behavior #4276

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2 changes: 1 addition & 1 deletion src/main/java/rx/internal/operators/OperatorDistinctUntilChanged.java
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Original file line number Diff line number Diff line change
Expand Up @@ -62,7 +62,7 @@ public OperatorDistinctUntilChanged(Func2<? super U, ? super U, Boolean> compara

@Override
public Boolean call(U t1, U t2) {
return (t1 == t2 || (t1 != null && t1.equals(t2)));
return (t1 == t2 || (t2 != null && t2.equals(t1)));
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Please add a test case that fails without fix and passed with it

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An example:
Object t1 and t2 are of the same type and contains an object x1.
Object x1 is null in t1 and is not null in t2
Object t1 and t2 override equals which in turn calls the equals of x1.
A NullpointerException is thrown from t1 but not from t2.

This is a basic example but what I want to say is that applying equals on t1 does not means that it will result the same the other way around.
That's the type of behavior changes which should be fixed on the user side of the rxjava lib but which can create confusion and can be avoided.

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The current comparison is completely legal, same as Java 7's Objects.equals(). Why did you swap the variables? Implementation of equals should be symmetric: a.equals(b) == b.equals(a).

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That's a broken equals implementation and not this library's problem.

}

@Override
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