Function derived

packages/svelte/src/internal/client/reactivity/deriveds.js:71–101

(fn)

 */
/*#__NO_SIDE_EFFECTS__*/
export function derived(fn) {
	var flags = DERIVED | DIRTY;

	if (active_effect !== null) {
		// Since deriveds are evaluated lazily, any effects created inside them are
		// created too late to ensure that the parent effect is added to the tree
		active_effect.f |= EFFECT_PRESERVED;
	}

	/** @type {Derived<V>} */
	const signal = {
		ctx: component_context,
		deps: null,
		effects: null,
		equals,
		f: flags,
		fn,
		reactions: null,
		rv: 0,
		v: /** @type {V} */ (UNINITIALIZED),
		wv: 0,
		parent: active_effect,
		ac: null
	};

	if (DEV && tracing_mode_flag) {
		signal.created = get_error('created at');
	}

	return signal;
}

export const OBSOLETE = Symbol('obsolete');