state provides a very simple mechanism for creating, manipulating, and listening to observable state in Go. All state is based around interface
type State[T any] interface {
Listen(func(T)) CancelFunc
}This registers a listener to be called when new values are available, and returns a function that deregisters the listener. The function is also called immediately with the current value of the state, and the Listen() method does not return until the passed function does.
Mutable state adds a Set(T) method that sets the current state and informs all of the listeners.
On top of these, a large number of utility functions are provided, most producing derived forms of state that modify the state in some way before passing it to listeners.