Make Cxx modules lazy on iOS

Reviewed By: mhorowitz

Differential Revision: D4716040

fbshipit-source-id: 08cc1317e15f0b3bd1df6d76c483a560f5c43d53

React/CxxBridge/RCTCxxBridge.mm

@@ -505,7 +505,7 @@ struct RCTInstanceCallback : public InstanceCallback {
       modules.emplace_back(std::make_unique<CxxNativeModule>(
         _reactInstance,
         [moduleData.name UTF8String],
-        [moduleData] { return [(RCTCxxModule *)(moduleData.instance) move]; },
+        [moduleData] { return [(RCTCxxModule *)(moduleData.instance) createModule]; },
         std::make_shared<DispatchMessageQueueThread>(moduleData)));
     } else {
       modules.emplace_back(std::make_unique<RCTNativeModule>(self, moduleData));

React/CxxModule/RCTCxxModule.h

@@ -14,14 +14,15 @@
 #import <React/RCTBridgeModule.h>
 #import <cxxreact/CxxModule.h>
 
+/**
+ * Subclass RCTCxxModule to use cross-platform CxxModule on iOS.
+ *
+ * Subclasses must implement the createModule method to lazily produce the module. When running under the Cxx bridge
+ * modules will be accessed directly, under the Objective-C bridge method access is wrapped through RCTCxxMethod.
+ */
 @interface RCTCxxModule : NSObject <RCTBridgeModule>
 
-- (instancetype)initWithCxxModule:(std::unique_ptr<facebook::xplat::module::CxxModule>)module;
-
-- (NSArray *)methodsToExport;
-- (NSDictionary *)constantsToExport;
-
-// Extracts the module from its objc wrapper
-- (std::unique_ptr<facebook::xplat::module::CxxModule>)move;
+// To be implemented by subclasses
+- (std::unique_ptr<facebook::xplat::module::CxxModule>)createModule;
 
 @end

React/CxxModule/RCTCxxModule.mm

@@ -23,37 +23,36 @@ using namespace facebook::react;
   std::unique_ptr<facebook::xplat::module::CxxModule> _module;
 }
 
-- (instancetype)init
-{
-  return nil;
-}
-
-- (instancetype)initWithCxxModule:(std::unique_ptr<facebook::xplat::module::CxxModule>)module
-{
-  RCTAssert([RCTBridgeModuleNameForClass([self class]) isEqualToString:@(module->getName().c_str())],
-            @"CxxModule class name %@ does not match runtime name %s",
-            RCTBridgeModuleNameForClass([self class]), module->getName().c_str());
-
-  if ((self = [super init])) {
-    _module = std::move(module);
-  }
-
-  return self;
-}
-
-- (std::unique_ptr<facebook::xplat::module::CxxModule>)move
-{
-  return std::move(_module);
-}
-
 + (NSString *)moduleName
 {
   return @"";
 }
 
-- (NSArray *)methodsToExport
+- (void)lazyInit
 {
-  CHECK(_module) << "Can't call methodsToExport on moved module";
+  if (!_module) {
+    _module = [self createModule];
+
+    if (_module) {
+      RCTAssert([RCTBridgeModuleNameForClass([self class]) isEqualToString:@(_module->getName().c_str())],
+                @"CxxModule class name %@ does not match runtime name %s",
+                RCTBridgeModuleNameForClass([self class]), _module->getName().c_str());
+    }
+  }
+}
+
+- (std::unique_ptr<facebook::xplat::module::CxxModule>)createModule
+{
+  RCTAssert(NO, @"Subclass %@ must override createModule", [self class]);
+  return nullptr;
+}
+
+- (NSArray<id<RCTBridgeMethod>> *)methodsToExport;
+{
+  [self lazyInit];
+  if (!_module) {
+    return nil;
+  }
 
   NSMutableArray *moduleMethods = [NSMutableArray new];
   for (const auto &method : _module->getMethods()) {
@@ -62,9 +61,12 @@ using namespace facebook::react;
   return moduleMethods;
 }
 
-- (NSDictionary *)constantsToExport
+- (NSDictionary<NSString *, id> *)constantsToExport;
 {
-  CHECK(_module) << "Can't call constantsToExport on moved module";
+  [self lazyInit];
+  if (!_module) {
+    return nil;
+  }
 
   NSMutableDictionary *moduleConstants = [NSMutableDictionary new];
   for (const auto &c : _module->getConstants()) {