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add changes() #115

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add changes() #115

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19 changes: 18 additions & 1 deletion src/Observables.jl
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
module Observables

export Observable, on, off, onany, connect!, obsid, async_latest, throttle
export Observable, on, off, onany, connect!, obsid, async_latest, throttle, changes
export Consume, ObserverFunction, AbstractObservable

import Base.Iterators.filter
Expand Down Expand Up @@ -572,6 +572,23 @@ Observable(3)
return obs
end

"""
changes(obs)

Returns an `Observable` that only forwards `obs` updates when its value changes.
"""
function changes(obs::AbstractObservable{T}) where {T}
result = Observable{T}(obs[])
oldobs = Observable{T}(obs[])
on(obs) do val
if val != oldobs[]
result[] = val
oldobs[] = val
end
end
return result
end


"""
async_latest(observable::AbstractObservable, n=1)
Expand Down