Documentation
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Overview ¶
Package settingswatch applies a value-typed settings section to a live consumer, re-applying whenever the section changes. It is the lightweight counterpart to observers like payloadlog's Controller: those own sink/emitter lifecycle and rebuild their own resources, whereas a Watcher just reads one section and hands the resolved value to an apply callback.
Use it for knobs whose runtime effect is "call this setter with the new value" (e.g. a parser toggle). The callback is where any vendor-specific or impure coupling lives, so the watcher itself stays vendor-neutral and testable.
The watcher is event-driven: it applies the current value once at Start and then re-applies on each settings-change callback from the Source — no polling. Because the callback fires on the catalog's serial NOTIFY goroutine, the apply must be cheap (it is, for a setter); a consumer with heavy work should use payloadlog's signal-a-goroutine pattern instead.
Index ¶
Constants ¶
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Variables ¶
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Functions ¶
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Types ¶
type Source ¶
type Source interface {
Setting(section string) (any, bool)
OnSettingsChange(section string, fn func())
}
Source is a live settings provider: read a section's current value and subscribe to its changes. Satisfied by *app/catalog.Catalog.
type Watcher ¶
type Watcher[T comparable] struct { // contains filtered or unexported fields }
Watcher applies one settings section to a consumer via an apply callback, on first Start and on every subsequent change. T is the section's value type; it must be comparable so change detection is a plain ==.
func New ¶
New builds a Watcher for section. apply is called with the resolved value at Start and on every change. If apply panics it is recovered and logged so a bad value can't take down the caller (or the catalog listener goroutine the change callback runs on).
func (*Watcher[T]) Start ¶
func (w *Watcher[T]) Start()
Start applies the current value once, then subscribes for changes. Synchronous and cheap; call it during composition after the catalog is wired. Reconcile order (apply-then-subscribe) guarantees at least one apply even if the section never changes; the mutex makes a change that races the initial apply safe.
Source Files