In one of my ObservableValue implementations I do have the need to decorate 
ChangeListener added to it.
Today this is somewhat complicated to implement, as I have to keep a map of the 
original listener to the decorated one to being able to handle the removal 
process of a listener. Because the outside World did not know that I decorated 
the listener and the instance passed in to removeListener ist the undecorated 

We can make things easier with a small change in 
ExpressionHelper.removeListener. When iterating through the listener list, the 
listener passed in as argument to removeListener is asked if it is equal to the 
one stored

                    if (listener.equals(changeListeners[index])) {

If we flip this to

                if (changeListeners[index].equals(listener)) {

a listener decoration can be smart enough to not only check against itself, but 
also against its delegate.

What do you think?

I could prepare a patch for the *ExpressionHelper classes.

Best regards,

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