Signals and derived values

A Signal[T] is any reactive value whose changes can be subscribed to. The interface is:

type Signal[T any] interface {
	Value() T
	// (unexported subscribe method used by the renderer)
}

Signals are produced by StateValue.Format and Derived.

Format signals

StateValue[T].Format(format) produces a Signal[string] by applying fmt.Sprintf(format, current). When you pass it to Text, the renderer subscribes and patches the label in place.

count := gova.State(s, 0)
 
gova.Text(count.Format("count: %d"))

Derived signals

Derived[T, U] transforms a *StateValue[T] into a Signal[U].

func Derived[T any, U any](state *StateValue[T], fn func(T) U) Signal[U]

The transformation runs eagerly once at creation time and again each time the source state changes.

type Model struct{ Todos []Todo }
 
model := gova.State(s, Model{})
 
total := gova.Derived(model, func(m Model) string {
    return fmt.Sprintf("%d items", len(m.Todos))
})
 
gova.Text(total)

Derived lists

DerivedList is a specialization that returns a *StateValue[[]T] instead of a Signal[[]T], so you can pass the result to List or ListOf.

func DerivedList[M any, T any](source *StateValue[M], extract func(M) []T) *StateValue[[]T]
 
todos := gova.DerivedList(model, func(m Model) []Todo { return m.Todos })

The derived state is read-only in practice; mutate the source state and the derived slice updates automatically.

Text accepts either a string or a Signal[string]

The Text constructor is Text(content any). It type-switches on the argument:

• string renders as static text.
• Signal[string] (produced by Format or Derived) renders reactively.

Any other type panics at construction time.