Feature request: off(o::AbstractObservable) off(o::AbstractObservable, index)

[hhaensel]

Hi everyone,

I have a project where I need to remove listeners from many observables.
Sometimes it's about removing all, sometimes about removing all except the first one.

I don't want to keep track of all the observer functions so I wondered whether it was possible to remove the listeners by index.
Hence I came up with the follwing code.

export off!, nlistener

nlistener(@nospecialize(o::Observable)) = length(Observables.listeners(o))

function off!(@nospecialize(o::Observables.AbstractObservable), index::Union{AbstractRange{<:Integer}, Vector{<:Integer}})
  allunique(index) || (@info("All indices must be distinct"); return BitVector(zeros(len)))

  len = length(index)
  callbacks = Observables.listeners(o)
  success = BitVector(zeros(len))

  for (i, n) in enumerate(reverse(sort(index)))
    if 0 < n <= length(callbacks)
      for g in Observables.removehandler_callbacks
        g(observable, callbacks[n])
      end
      deleteat!(callbacks, n)
      success[len - i + 1] = true
    end
  end

  success
end

off!(@nospecialize(o::Observables.AbstractObservable), index::Integer) = off!(o, [index])[1]

off!(@nospecialize(o::Observables.AbstractObservable)) = off!(o, 1:length(Observables.listeners(o)))

Does that look like something you'd like to integrate in Observables?

If so, please let me know. I'd be happy to submit a PR.