RGA

Replicated Growable Array. Conflict-free ordered sequence for collaborative text editing.

An RGA (Replicated Growable Array) is an ordered sequence CRDT designed for collaborative text editing. Concurrent inserts and deletes from multiple clients converge to the same result without conflicts.

Each character is assigned a unique identifier at insert time. Deletions are soft (tombstoned) and removed from the visible value. Concurrent inserts at the same position are deterministically ordered by author ID.

Usage

const doc = client.rga("rg:doc-123");

// Insert at position
doc.insert(0, "Hello");
doc.insert(5, " world");

// Delete characters
doc.delete(5, 6); // delete " world"

console.log(doc.value()); // "Hello"

doc.onChange(text => console.log("text:", text));

React

import { useRGA } from "meridian-react";

function Editor() {
  const { value, insert, delete: del } = useRGA("rg:doc-123");

  const handleChange = (e: React.ChangeEvent<HTMLTextAreaElement>) => {
    const newText = e.target.value;
    // Simple diff: replace all (for demo — use a proper diff for production)
    del(0, value.length);
    insert(0, newText);
  };

  return <textarea value={value} onChange={handleChange} />;
}

Effect stream

import { Stream, Effect } from "effect";

await Effect.runPromise(
  doc.stream().pipe(
    Stream.runForEach(text => Effect.log(`doc: ${text}`))
  )
);

API

Method	Description
insert(pos: number, text: string, ttlMs?)	Insert characters at position
delete(pos: number, length: number, ttlMs?)	Delete length characters starting at pos
value()	Returns current text as string
onChange(fn)	Subscribe — returns unsubscribe function
stream()	Returns an Effect Stream<string> that emits on every change

Conflict semantics

• Concurrent inserts at the same position are ordered by author ID (deterministic, total order)
• Concurrent delete + insert: the insert survives — deletions only remove characters that existed at the time of the delete op
• Idempotent: applying the same op twice has no effect

CRDT key prefix

Use the rg: prefix by convention:

const doc = client.rga("rg:document-42");