Is it possible to create a Setter which does nothing? Simply returns the source without any changes....

# arrow

[dimsuz]

Is it possible to create a Setter which does nothing? Simply returns the source without any changes. Or will this be an unlawful optic?

[Alejandro Serrano.Mena]

that won't satisfy the "get after set" rule

lens.get(lens.set(x, v)) == v

[dimsuz]

Right!

In my case though I don't need lens, only the setter. I have an utility function which sets the "progressBarVisible" in the UI State, but some UI States do not have this progress bar, so I wanted a Setter which does nothing, e.g.

@optics
data class UiState1(title: String, progressBarVisible: Boolean)
@optics
data class UiState2(title: String)

and then

cleverUpdate(
  titleLens = UiState1.title,
  progressBarVisibleSetter = UiState1.progressBarVisible
)

and I wondered what to do for UiState2 here.
But after I asked the question I discovered I could do this:

cleverUpdate(
  titleLens = UiState2.title,
  progressBarVisibleSetter = { state, _ -> state } // this is a PSetter too
)