id_pair_set

One thing, many identifiers. id_pair_set holds the ids an entity answers to — an ISBN, a UPC, a manufacturer's part number, your own SKU — as an immutable set keyed by id type, so each namespace contributes at most one code.

Why

The same physical thing is named differently by everyone who touches it. A part number from Bally, another from Stern, a publisher's reference, our own SKU. Kept as loose strings, those aliases drift into prose and importer code and nobody can tell whether two ids mean the same object. Kept as pairs keyed by namespace, the identity is one value: comparable, serializable, and impossible to duplicate by accident.

The model

• IdPair<T> — one identifier: an idType (the namespace) and an idCode. Equality is both fields, so pairs compare by content. Subclass it when ids are keyed by an enum; the type is preserved, not dynamic.
• SimpleIdPair — the common case, namespaced by a plain string.
• IdPairSet<T> — an immutable set holding at most one pair per id type, with operator [] lookup, contains/containsType/containsCode, add, addAll, remove, removeType and pairs/idTypes/length readers.
• DuplicatePolicy — firstWins or lastWins, applied when two pairs claim the same type.

Guarantees

• Nothing is dropped quietly. A pair displaced by a duplicate id type is reported by duplicates (hasDuplicates for the boolean), so a loader can refuse the data and a merge can see which occurrence lost. There is no keep-silently mode.
• Equality is by content, not insertion order. Two sets holding the same pairs are equal and hash equal however they were built, so change detection and diff gates fire on real changes only.
• One wire format, and it round-trips. toJson writes a {idType: idCode} object; fromPlainJson reads the string-keyed form back and fromJson takes a builder for enum-keyed pairs. toString is a sorted rendering for logs and labels — display only, never parsed.
• No exceptions. Nothing here can fail: a malformed entry is a value, not a throw, so callers decide what to do with it.

Usage

The runnable example is example/main.dart (CI runs it on every push), and the tests in test/ are the reference for every behaviour above.

Add id_pair_set: ^2.0.0 to your pubspec.

Upgrading from 1.x

IdPairSet was rebuilt in 2.0.0: dynamic idType became IdPair<T>, the keepLast flag became DuplicatePolicy, idPairs became pairs, getByType became operator [], and toString is documented as display-only now that toJson/fromPlainJson exist. The 2.0.0 section of CHANGELOG.md lists every rename.

Related

id_registry builds on this package to check uniqueness across many sets.

License

MIT. See LICENSE.