ZState[S] models a value of type S that can be read from and written to during the execution of an effect. The idiomatic way to work with ZState is as part of the environment using operators defined on ZIO. For example:

final case class MyState(counter: Int)

for {
  _     <- ZIO.updateState[MyState](state => state.copy(counter = state.counter + 1))
  count <- ZIO.getStateWith[MyState](_.counter)
} yield count

Because ZState is typically used as part of the environment, it is recommended to define your own state type S such as MyState above rather than using a type such as Int to avoid the risk of ambiguity.

To run an effect that depends on some state, create the initial state with the make constructor and then use toLayer to convert it into a layer that you can provide along with your application's other dependencies.