@here.build/collections

Map/WeakMap collection utilities with default-value semantics, plus optional MobX-reactive computed variants.

Install

pnpm add @here.build/collections

Usage

import { DefaultedMap, Counter } from "@here.build/collections";

const groups = new DefaultedMap<string, string[]>(() => []);
groups.get("a").push("x");   // auto-creates the array

const counts = new Counter<string>();
counts.add("hit");

• DefaultedMap / DefaultedWeakMap — get auto-creates a missing entry from a factory.
• Counter — tally occurrences.
• PathMap — tuple/path keys.
• ArrayMultimap / SetMultimap — one key, many values.
• ordinal — process-local, pointer-identity object handles (see below).
• /mobx subpath — ComputedMap, ComputedWeakMap, ComputedUniformMap: MobX-reactive computed variants.

ordinal — process-local object identity

import { ordinal } from "@here.build/collections";

ordinal.id(obj);          // stable monotonic int, assigned on first sight, cached in a WeakMap
ordinal.sort(a, b);       // total order: objects by their ordinal, primitives by type then value

• ordinal.id(o) — a stable handle for an object keyed off its pointer identity. Assigned the first time it sees o and returned unchanged forever after. Never serialized, never crosses a process boundary — it only has to be consistent within a session, not meaningful. Use it to key a Map by reference, or to give an unordered Set a canonical order, without inventing a serialized id.
• ordinal.sort(a, b) — a comparator using ordinal.id for objects and type-then-value for primitives.

Pairs naturally with anything that guarantees singleton objects (one stable object per logical thing): the ordinal then becomes a reliable session-local id for a thing that has no shared id of its own yet.

import { ComputedMap } from "@here.build/collections/mobx";

License

MIT