dynamicDerived()

Like derived(), but dependencies are discovered at runtime via a tracking get function. Deps can change between recomputations — upstream connections are rewired automatically.

Participates in diamond resolution (Tier 1). Same lazy lifecycle as derived: no computation until first subscriber or .get() call; disconnects from deps when the last subscriber leaves.

Signature

function dynamicDerived<T>(fn: (get: TrackingGet) => T, opts?: DerivedOptions<T>): Store<T>

• fn receives a tracking get(store) function. Every store accessed via get() becomes a dependency for that recomputation.
• Dependencies are re-discovered on every recomputation. If get(flag) causes a branch that skips get(b), b is not subscribed.

Usage

import { state, dynamicDerived } from 'callbag-recharge'

const flag = state(true)
const a = state(1)
const b = state(2)

const result = dynamicDerived((get) => {
  return get(flag) ? get(a) : get(b)
})

result.get() // 1 — deps: [flag, a]
flag.set(false)
result.get() // 2 — deps rewired to [flag, b]; no longer subscribed to a

Options

Option	Type	Default	Description
equals	(a, b) => boolean	Object.is	Push-phase memoization. Sends RESOLVED instead of DATA if value is unchanged.
name	string	—	Debug name shown in Inspector.

vs derived()

	derived	dynamicDerived
Dep declaration	Explicit array [dep1, dep2]	Runtime via get()
Dep changes	Fixed at construction	Rewired on each recomputation
Use when	Deps are statically known	Deps depend on runtime values (e.g. conditional, lookup tables)
Overhead	None	Small per-recompute rewire check

Notes

• Re-entrancy guard (D_RECOMPUTING flag) prevents signal cycles during dep rewire.
• Stores not accessed in the latest fn() call are automatically unsubscribed.
• derived.from(dep) is the identity shorthand for single-dep forwarding — use derived or dynamicDerived for transform cases.
• Pull-computes from deps when DISCONNECTED (no subscribers). get() is always fresh.

See also

• derived() — explicit-dep computed store
• effect() — side-effect runner with same dep model
• Architecture §4 — Transform nodes