prelim refactor commit

src/structs/AbstractStruct.js

@@ -0,0 +1,38 @@
+import { Y } from '../utils/Y.js' // eslint-disable-line
+import { ID } from '../utils/ID.js' // eslint-disable-line
+import { Transaction } from '../utils/Transaction.js' // eslint-disable-line
+
+// eslint-disable-next-line
+export class AbstractStruct {
+  /**
+   * @param {ID} id
+   */
+  constructor (id) {
+    /**
+     * The uniqe identifier of this struct.
+     * @type {ID}
+     * @readonly
+     */
+    this.id = id
+  }
+  /**
+   * @type {number}
+   */
+  get length () {
+    throw new Error('unimplemented')
+  }
+}
+
+export class AbstractRef {
+  /**
+   * @return {Array<ID|null>}
+   */
+  getMissing () {
+    return []
+  }
+  /**
+   * @param {Transaction} transaction
+   * @return {AbstractStruct}
+   */
+  toStruct (transaction) { throw new Error('Must be defined') }
+}