ReactorComputationFunction to run when this computation is next invalidated,
or runs it immediately if the computation is already invalidated.ReactorComputationFunction now and rerun it later whenever its dependencies change.ReactorComputation if given) depends on `dependency`.ReactorComputation,
which would be invalidated if this ReactorDependency were to change.ReactorComputationFunction react on the current computation (which must exist),
to be called immediately when the current computation is invalidated or stopped.ReactorDependency
If you'd like to use primitive data types, you'll have to handle your own instance of
ReactorDependency alongside your primitive value
Created by vishnu on 1/25/15.