2. Derived values — computed

When a value is computed from other signals, don't recompute it by hand — wrap it in computed. It tracks what it reads, caches the result, and recomputes only when a dependency actually changes.

import { signal, computed } from '@pyreon/reactivity'

const first = signal('Ada')
const last = signal('Lovelace')
const full = computed(() => `${first()} ${last()}`) // re-derives when either changes

full() // 'Ada Lovelace'

A computed reads like a signal (call it: full()), but you never write to it — it's derived. Try it:

The key idea: computed is lazy and cached. Reading full() repeatedly does the work once; it only re-runs when first or last changes. Reach for it whenever you'd otherwise duplicate a derivation.

A computed is roughly 10× the memory of a plain signal (it caches + tracks). Use it for real derivations, not as a fancy alias for a value you could just read.

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