more efficient length computing

structs/Item.js

@@ -251,16 +251,22 @@ export class Item {
    */
   _delete (y, createDelete = true, gcChildren) {
     if (!this._deleted) {
+      const parent = this._parent
+      const len = this._length
+      // adjust the length of parent
+      if (parent.length !== undefined && this._countable) {
+        parent.length -= len
+      }
       this._deleted = true
       y.ds.mark(this._id, this._length, false)
       let del = new Delete()
       del._targetID = this._id
-      del._length = this._length
+      del._length = len
       if (createDelete) {
         // broadcast and persists Delete
         del._integrate(y, true)
       }
-      transactionTypeChanged(y, this._parent, this._parentSub)
+      transactionTypeChanged(y, parent, this._parentSub)
       y._transaction.deletedStructs.add(this)
     }
   }
@@ -410,6 +416,10 @@ export class Item {
         right._left = this
       }
     }
+    // adjust the length of parent
+    if (parent.length !== undefined && this._countable) {
+      parent.length += this._length
+    }
     if (parent._deleted) {
       this._delete(y, false, true)
     }

tests/helper.js

@@ -313,9 +313,11 @@ export const compareUsers = (t, users) => {
   })
   for (var i = 0; i < data.length - 1; i++) {
     t.group(() => {
+      t.compare(userArrayValues[i].length, users[i].get('array').length, 'array length correctly computed')
       t.compare(userArrayValues[i], userArrayValues[i + 1], 'array types')
       t.compare(userMapValues[i], userMapValues[i + 1], 'map types')
       t.compare(userXmlValues[i], userXmlValues[i + 1], 'xml types')
+      t.compare(userTextValues[i].map(a => a.insert).join('').length, users[i].get('text').length, 'text length correctly computed')
       t.compare(userTextValues[i], userTextValues[i + 1], 'text types')
       t.compare(userQuillValues[i], userQuillValues[i + 1], 'quill delta content')
       t.compare(data[i].os, data[i + 1].os, 'os')

types/YArray.js

@@ -72,6 +72,10 @@ export class YArrayEvent extends YEvent {
  * A shared Array implementation.
  */
 export class YArray extends Type {
+  constructor () {
+    super()
+    this.length = 0
+  }
   /**
    * Creates YArray Event and calls observers.
    *
@@ -167,21 +171,6 @@ export class YArray extends Type {
     }
   }
 
-  /**
-   * Computes the length of this YArray.
-   */
-  get length () {
-    let length = 0
-    let n = this._start
-    while (n !== null) {
-      if (!n._deleted && n._countable) {
-        length += n._length
-      }
-      n = n._right
-    }
-    return length
-  }
-
   [Symbol.iterator] () {
     return {
       next: function () {