Removing a child observable

[ffreyer]

As far as I can tell there is no automatic way to remove a child observable and detach it from all its parents. For example

O1 = Observable(1)
O2 = map(identity, O1)
O2 = nothing
GC.gc()

will leave you with a listener in O1 and O2 will remain somewhere in memory. The same happens with weak = true - the mapped observable and the listeners remain. In these cases one can explicitly remove listener with off.(O2.inputs), which then allows them to be gced.

With on it's a bit different. There are no references being kept in inputs for on, so the above doesn't work. The gc will also happily remove the observable when it goes out of scope, causing this to error:

O1 = Observable(1)
O2 = Observable(1)
on(x -> O2[] = x, O1)
O2 = nothing
O1[] = 1

So in this case one would need to keep track of observer functions themselves to correctly remove a child. It would be nice if this was easier to handle.

[timholy]

xref #69. I don't currently have the bandwidth to tackle this but it's probably the one remaining big issue for this package to address.