Filter

.filter (Publishers.Filter) takes a function (the filter function) that receives the published value from upstream and stops it from proceeding further down the pipeline unless it passes some test. The function returns a Bool saying whether the value should be permitted to proceed down the pipeline. Think of a filter as a map to nothing.

In this (rather silly) example, we’re running a Timer, but there’s also a UISwitch mySwitch in our interface, and if the UISwitch is off, no Timer firing signals get through the pipeline:

Timer.publish(every: 1, on: .main, in: .default)
    .autoconnect()
    .filter {_ in self.mySwitch.isOn}

There is also a .tryFilter (Publishers.TryFilter); it works similarly to .tryMap, so I won’t say more about it.