Make structures for data stores extensible

src/index.js

@@ -18,6 +18,7 @@ module.exports = {
   Permissions: require('./util/Permissions'),
   Snowflake: require('./util/Snowflake'),
   SnowflakeUtil: require('./util/Snowflake'),
+  Structures: require('./util/Structures'),
   Util: Util,
   util: Util,
   version: require('../package.json').version,

src/stores/DataStore.js

@@ -1,4 +1,5 @@
 const Collection = require('../util/Collection');
+const Structures = require('../util/Structures');
 
 /**
  * Manages the creation, retrieval and deletion of a specific data model.
@@ -8,7 +9,7 @@ class DataStore extends Collection {
   constructor(client, iterable, holds) {
     super();
     Object.defineProperty(this, 'client', { value: client });
-    Object.defineProperty(this, 'holds', { value: holds });
+    Object.defineProperty(this, 'holds', { value: Structures.get(holds.name) });
     if (iterable) for (const item of iterable) this.create(item);
   }
 

src/util/Structures.js

@@ -0,0 +1,54 @@
+/**
+ * Allows for the extension of built-in Discord.js structures that are instantiated by {@link DataStore}s.
+ * When extending a built-in structure, it is important to both get the class you're extending from here,
+ * and to set it here afterwards.
+ * @example
+ * const { Structures } = require('discord.js);
+ *
+ * class CoolGuild extends Structures.get('Guild') {
+ *   constructor(client, data) {
+ *     super(client, data);
+ *     this.cool = true;
+ *   }
+ * }
+ *
+ * Structures.set('Guild', CoolGuild);
+ */
+class Structures {
+  constructor() {
+    throw new Error(`The ${this.constructor.name} class may not be instantiated.`);
+  }
+
+  /**
+   * Retrieves a structure class.
+   * @param {string} name Name of the base structure
+   * @returns {Function}
+   */
+  static get(name) {
+    return structures[name];
+  }
+
+  /**
+   * Overrides a structure class.
+   * @param {string} name Name of the base structure
+   * @param {Function} custom Extended structure class to override with
+   */
+  static set(name, custom) {
+    structures[name] = custom;
+  }
+}
+
+const structures = {
+  Channel: require('./structures/Channel'),
+  Emoji: require('./structures/Emoji'),
+  GuildChannel: require('./structures/GuildChannel'),
+  GuildMember: require('./structures/GuildMember'),
+  Guild: require('./structures/Guild'),
+  Message: require('./structures/Message'),
+  Presence: require('./structures/Presence'),
+  Reaction: require('./structures/Reaction'),
+  Role: require('./structures/Role'),
+  User: require('./structures/User'),
+};
+
+module.exports = Structures;