RgaList<T> class

A Replicated Growable Array (RGA) — a convergent ordered-sequence CRDT.

This is the sequence type collaborative editors need: concurrent inserts and deletes on different devices merge deterministically without dropping elements. Each element is identified by (replicaId, counter) and anchored after the element it was inserted behind; concurrent inserts at the same anchor are ordered by Lamport counter (newest first), so every replica arrives at the same order from the same element set.

Like the other CRDTs in this file it is immutable — operations return a new list — and merging is a state-based union (commutative, associative, idempotent):

var a = RgaList<String>(replicaId: 'device-a').insertAll(0, ['h', 'i']);
var b = RgaList<String>.fromMap(a.toMap(), (v) => v as String, replicaId: 'device-b');

a = a.insert(2, '!');            // device A appends '!'
b = b.insert(0, '>');            // device B prepends '>'

final mergedA = a.merge(b);
final mergedB = b.merge(a);
assert(mergedA.value.join() == mergedB.value.join()); // '>hi!'

Contiguous runs inserted with insertAll (or RgaText.insert) chain each element to the previous one, so two devices typing words concurrently at the same spot do not interleave characters.

Implemented types

Constructors

RgaList({required String replicaId})
Creates an empty sequence owned by replicaId.
const
RgaList.fromMap(Map<String, dynamic> map, T decoder(dynamic raw), {String? replicaId})
Deserializes a sequence.
factory

Properties

hashCode → int
The hash code for this object.
no setterinherited
idsInOrder → List<String>
The visible element ids in order — stable handles for cursor positions.
no setter
isEmpty → bool
Whether the sequence has no visible elements.
no setter
length → int
Number of visible elements.
no setter
props → List<Object?>
The list of properties that will be used to determine whether two instances are equal.
no setter
replicaId → String
This replica's identity, stamped on locally created elements.
final
runtimeType → Type
A representation of the runtime type of the object.
no setterinherited
stringify → bool?
If set to true, the toString method will be overridden to output this instance's props.
no setterinherited
tombstoneCount → int
Number of tombstoned elements retained for ordering (see compacted).
no setter
value → List<T>
The visible (non-tombstoned) elements, in convergent order.
no setteroverride

Methods

add(T element) → RgaList<T>
Appends element at the end of the sequence.
compacted() → RgaList<T>
Returns a copy with every tombstone purged.
elementIdAt(int index) → String
The id of the visible element at index.
indexOfId(String id) → int
The visible index of element id, or -1 if absent/tombstoned.
insert(int index, T element) → RgaList<T>
Inserts element at visible index (0 = head, length = append).
insertAll(int index, Iterable<T> elements) → RgaList<T>
Inserts elements as a contiguous run at visible index.
merge(covariant RgaList<T> other) → RgaList<T>
Merges this CRDT with another of the same type.
override
noSuchMethod(Invocation invocation) → dynamic
Invoked when a nonexistent method or property is accessed.
inherited
removeAt(int index) → RgaList<T>
Tombstones the visible element at index.
removeById(String id) → RgaList<T>
Tombstones the element with id (no-op if unknown).
removeRange(int index, int count) → RgaList<T>
Tombstones count visible elements starting at index.
toMap() → Map<String, dynamic>
Converts the CRDT state to a map for serialization.
override
toString() → String
A string representation of this object.

Operators

operator ==(Object other) → bool
The equality operator.
inherited