Cast

Author: schmidt-sebastian

packages/firestore/src/remote/datastore.ts

@@ -20,7 +20,7 @@ import { MaybeDocument } from '../model/document';
 import { DocumentKey } from '../model/document_key';
 import { Mutation, MutationResult } from '../model/mutation';
 import * as api from '../protos/firestore_proto_api';
-import { debugAssert, hardAssert } from '../util/assert';
+import { debugCast, hardAssert } from '../util/assert';
 import { Code, FirestoreError } from '../util/error';
 import { Connection } from './connection';
 import { JsonProtoSerializer } from './serializer';
@@ -102,11 +102,7 @@ export async function invokeCommitRpc(
   datastore: Datastore,
   mutations: Mutation[]
 ): Promise<MutationResult[]> {
-  debugAssert(
-    datastore instanceof DatastoreImpl,
-    'invokeCommitRpc() requires DatastoreImpl'
-  );
-  const datastoreImpl: DatastoreImpl = datastore;
+  const datastoreImpl = debugCast(datastore, DatastoreImpl);
   const params = {
     database: datastoreImpl.serializer.encodedDatabaseId,
     writes: mutations.map(m => datastoreImpl.serializer.toMutation(m))
@@ -125,11 +121,7 @@ export async function invokeBatchGetDocumentsRpc(
   datastore: Datastore,
   keys: DocumentKey[]
 ): Promise<MaybeDocument[]> {
-  debugAssert(
-    datastore instanceof DatastoreImpl,
-    'invokeBatchGetDocumentsRpc() requires DatastoreImpl'
-  );
-  const datastoreImpl: DatastoreImpl = datastore;
+  const datastoreImpl = debugCast(datastore, DatastoreImpl);
   const params = {
     database: datastoreImpl.serializer.encodedDatabaseId,
     documents: keys.map(k => datastoreImpl.serializer.toName(k))
@@ -158,11 +150,7 @@ export function newPersistentWriteStream(
   queue: AsyncQueue,
   listener: WriteStreamListener
 ): PersistentWriteStream {
-  debugAssert(
-    datastore instanceof DatastoreImpl,
-    'newPersistentWriteStream() requires DatastoreImpl'
-  );
-  const datastoreImpl: DatastoreImpl = datastore;
+  const datastoreImpl = debugCast(datastore, DatastoreImpl);
   return new PersistentWriteStream(
     queue,
     datastoreImpl.connection,
@@ -177,11 +165,7 @@ export function newPersistentWatchStream(
   queue: AsyncQueue,
   listener: WatchStreamListener
 ): PersistentListenStream {
-  debugAssert(
-    datastore instanceof DatastoreImpl,
-    'newPersistentWatchStream() requires DatastoreImpl'
-  );
-  const datastoreImpl: DatastoreImpl = datastore;
+  const datastoreImpl = debugCast(datastore, DatastoreImpl);
   return new PersistentListenStream(
     queue,
     datastoreImpl.connection,

packages/firestore/src/util/assert.ts

@@ -70,3 +70,19 @@ export function debugAssert(
     fail(message);
   }
 }
+
+/**
+ * Casts `obj` to `T`. In non-production builds, verifies that `obj` is an
+ * instance of `T` before casting.
+ */
+export function debugCast<T>(
+  obj: object,
+  // eslint-disable-next-line @typescript-eslint/no-explicit-any
+  constructor: { new (...args: any[]): T }
+): T {
+  debugAssert(
+    obj instanceof constructor,
+    `Expected type '${constructor.name}', but was '${obj.constructor.name}'`
+  );
+  return obj as T;
+}

packages/firestore/test/unit/util/misc.test.ts

@@ -17,10 +17,27 @@
 
 import { expect } from 'chai';
 import { immediateSuccessor } from '../../../src/util/misc';
+import { debugCast } from '../../../src/util/assert';
 
 describe('immediateSuccessor', () => {
   it('generates the correct immediate successors', () => {
     expect(immediateSuccessor('hello')).to.equal('hello\0');
     expect(immediateSuccessor('')).to.equal('\0');
   });
 });
+
+describe('typeCast', () => {
+  it('can cast types', () => {
+    class Foo {}
+    class Bar extends Foo {}
+    const foo: Foo = new Bar();
+    const bar: Bar = debugCast(foo, Bar);
+  });
+
+  it.only('validates types', () => {
+    class Foo {}
+    class Bar {}
+    const foo = new Foo();
+    expect(debugCast(foo, Bar)).to.throw("Expected type 'Bar', but was 'Foo'");
+  });
+});