Improve memory usage by omitting the ItemRef step and directly applying the Item

src/structs/GC.js

@@ -1,12 +1,10 @@
 
 import {
-  AbstractStructRef,
   AbstractStruct,
   addStruct,
   StructStore, Transaction, ID // eslint-disable-line
 } from '../internals.js'
 
-import * as decoding from 'lib0/decoding.js'
 import * as encoding from 'lib0/encoding.js'
 
 export const structGCRefNumber = 0
@@ -37,8 +35,13 @@ export class GC extends AbstractStruct {
 
   /**
    * @param {Transaction} transaction
+   * @param {number} offset
    */
-  integrate (transaction) {
+  integrate (transaction, offset) {
+    if (offset > 0) {
+      this.id.clock += offset
+      this.length -= offset
+    }
     addStruct(transaction.doc.store, this)
   }
 
@@ -50,39 +53,13 @@ export class GC extends AbstractStruct {
     encoding.writeUint8(encoder, structGCRefNumber)
     encoding.writeVarUint(encoder, this.length - offset)
   }
-}
-
-/**
- * @private
- */
-export class GCRef extends AbstractStructRef {
-  /**
-   * @param {decoding.Decoder} decoder
-   * @param {ID} id
-   * @param {number} info
-   */
-  constructor (decoder, id, info) {
-    super(id)
-    /**
-     * @type {number}
-     */
-    this.length = decoding.readVarUint(decoder)
-  }
 
   /**
    * @param {Transaction} transaction
    * @param {StructStore} store
-   * @param {number} offset
-   * @return {GC}
+   * @return {null | ID}
    */
-  toStruct (transaction, store, offset) {
-    if (offset > 0) {
-      this.id.clock += offset
-      this.length -= offset
-    }
-    return new GC(
-      this.id,
-      this.length
-    )
+  getMissing (transaction, store) {
+    return null
   }
 }