src: add templated function factories

These variants of `Napi::Function::New` accept the callback as a template parameter rather than a function parameter. This allows us to perform the binding without additional heap-allocation of the function callback data. PR-URL: nodejs/node-addon-api#608 Reviewed-By: Nicola Del Gobbo <nicoladelgobbo@gmail.com> Reviewed-By: Chengzhong Wu <legendecas@gmail.com> Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
johnfrench3 · Dec 14, 2019 · 9a7e48e · 9a7e48e
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diff --git a/doc/function.md b/doc/function.md
@@ -25,7 +25,7 @@ Value Fn(const CallbackInfo& info) {
 }
 
 Object Init(Env env, Object exports) {
-  exports.Set(String::New(env, "fn"), Function::New(env, Fn));
+  exports.Set(String::New(env, "fn"), Function::New<Fn>(env));
 }
 
 NODE_API_MODULE(NODE_GYP_MODULE_NAME, Init)
@@ -47,6 +47,27 @@ and in general in situations which don't have an existing JavaScript function on
 the stack. The `Call` method is used when there is already a JavaScript function
 on the stack (for example when running a native method called from JavaScript).
 
+## Type definitions
+
+### Napi::Function::VoidCallback
+
+This is the type describing a callback returning `void` that will be invoked
+from JavaScript.
+
+```cpp
+typedef void (*VoidCallback)(const Napi::CallbackInfo& info);
+```
+
+### Napi::Function::Callback
+
+This is the type describing a callback returning a value that will be invoked
+from JavaScript.
+
+
+```cpp
+typedef Value (*Callback)(const Napi::CallbackInfo& info);
+```
+
 ## Methods
 
 ### Constructor
@@ -74,6 +95,86 @@ Returns a non-empty `Napi::Function` instance.
 
 Creates an instance of a `Napi::Function` object.
 
+```cpp
+template <Napi::VoidCallback cb>
+static Napi::Function New(napi_env env,
+                          const char* utf8name = nullptr,
+                          void* data = nullptr);
+```
+
+- `[template] cb`: The native function to invoke when the JavaScript function is
+invoked.
+- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
+- `[in] utf8name`: Null-terminated string to be used as the name of the function.
+- `[in] data`: User-provided data context. This will be passed back into the
+function when invoked later.
+
+Returns an instance of a `Napi::Function` object.
+
+### New
+
+Creates an instance of a `Napi::Function` object.
+
+```cpp
+template <Napi::Callback cb>
+static Napi::Function New(napi_env env,
+                          const char* utf8name = nullptr,
+                          void* data = nullptr);
+```
+
+- `[template] cb`: The native function to invoke when the JavaScript function is
+invoked.
+- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
+- `[in] utf8name`: Null-terminated string to be used as the name of the function.
+- `[in] data`: User-provided data context. This will be passed back into the
+function when invoked later.
+
+Returns an instance of a `Napi::Function` object.
+
+### New
+
+Creates an instance of a `Napi::Function` object.
+
+```cpp
+template <Napi::VoidCallback cb>
+static Napi::Function New(napi_env env,
+                          const std::string& utf8name,
+                          void* data = nullptr);
+```
+
+- `[template] cb`: The native function to invoke when the JavaScript function is
+invoked.
+- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
+- `[in] utf8name`: String to be used as the name of the function.
+- `[in] data`: User-provided data context. This will be passed back into the
+function when invoked later.
+
+Returns an instance of a `Napi::Function` object.
+
+### New
+
+Creates an instance of a `Napi::Function` object.
+
+```cpp
+template <Napi::Callback cb>
+static Napi::Function New(napi_env env,
+                          const std::string& utf8name,
+                          void* data = nullptr);
+```
+
+- `[template] cb`: The native function to invoke when the JavaScript function is
+invoked.
+- `[in] env`: The `napi_env` environment in which to construct the `Napi::Function` object.
+- `[in] utf8name`: String to be used as the name of the function.
+- `[in] data`: User-provided data context. This will be passed back into the
+function when invoked later.
+
+Returns an instance of a `Napi::Function` object.
+
+### New
+
+Creates an instance of a `Napi::Function` object.
+
 ```cpp
 template <typename Callable>
 static Napi::Function Napi::Function::New(napi_env env, Callable cb, const char* utf8name = nullptr, void* data = nullptr);

diff --git a/napi-inl.h b/napi-inl.h
@@ -1766,6 +1766,51 @@ CreateFunction(napi_env env,
   return status;
 }
 
+template <Function::VoidCallback cb>
+inline Function Function::New(napi_env env, const char* utf8name, void* data) {
+  napi_value result = nullptr;
+  napi_status status = napi_create_function(
+      env, utf8name, NAPI_AUTO_LENGTH,
+      [](napi_env env, napi_callback_info info) {
+        CallbackInfo callbackInfo(env, info);
+        return details::WrapCallback([&] {
+          cb(callbackInfo);
+          return nullptr;
+        });
+      }, data, &result);
+  NAPI_THROW_IF_FAILED(env, status, Function());
+  return Function(env, result);
+}
+
+template <Function::Callback cb>
+inline Function Function::New(napi_env env, const char* utf8name, void* data) {
+  napi_value result = nullptr;
+  napi_status status = napi_create_function(
+      env, utf8name, NAPI_AUTO_LENGTH,
+      [](napi_env env, napi_callback_info info) {
+        CallbackInfo callbackInfo(env, info);
+        return details::WrapCallback([&] {
+          return cb(callbackInfo);
+        });
+      }, data, &result);
+  NAPI_THROW_IF_FAILED(env, status, Function());
+  return Function(env, result);
+}
+
+template <Function::VoidCallback cb>
+inline Function Function::New(napi_env env,
+                              const std::string& utf8name,
+                              void* data) {
+  return Function::New<cb>(env, utf8name.c_str(), data);
+}
+
+template <Function::Callback cb>
+inline Function Function::New(napi_env env,
+                              const std::string& utf8name,
+                              void* data) {
+  return Function::New<cb>(env, utf8name.c_str(), data);
+}
+
 template <typename Callable>
 inline Function Function::New(napi_env env,
                               Callable cb,

diff --git a/napi.h b/napi.h
@@ -993,6 +993,29 @@ namespace Napi {
 
   class Function : public Object {
   public:
+    typedef void (*VoidCallback)(const CallbackInfo& info);
+    typedef Value (*Callback)(const CallbackInfo& info);
+
+    template <VoidCallback cb>
+    static Function New(napi_env env,
+                        const char* utf8name = nullptr,
+                        void* data = nullptr);
+
+    template <Callback cb>
+    static Function New(napi_env env,
+                        const char* utf8name = nullptr,
+                        void* data = nullptr);
+
+    template <VoidCallback cb>
+    static Function New(napi_env env,
+                        const std::string& utf8name,
+                        void* data = nullptr);
+
+    template <Callback cb>
+    static Function New(napi_env env,
+                        const std::string& utf8name,
+                        void* data = nullptr);
+
     /// Callable must implement operator() accepting a const CallbackInfo&
     /// and return either void or Value.
     template <typename Callable>

diff --git a/test/function.cc b/test/function.cc
@@ -105,6 +105,7 @@ void IsConstructCall(const CallbackInfo& info) {
 } // end anonymous namespace
 
 Object InitFunction(Env env) {
+  Object result = Object::New(env);
   Object exports = Object::New(env);
   exports["voidCallback"] = Function::New(env, VoidCallback, "voidCallback");
   exports["valueCallback"] = Function::New(env, ValueCallback, std::string("valueCallback"));
@@ -120,5 +121,29 @@ Object InitFunction(Env env) {
   exports["callConstructorWithArgs"] = Function::New(env, CallConstructorWithArgs);
   exports["callConstructorWithVector"] = Function::New(env, CallConstructorWithVector);
   exports["isConstructCall"] = Function::New(env, IsConstructCall);
-  return exports;
+  result["plain"] = exports;
+
+  exports = Object::New(env);
+  exports["voidCallback"] = Function::New<VoidCallback>(env, "voidCallback");
+  exports["valueCallback"] =
+      Function::New<ValueCallback>(env, std::string("valueCallback"));
+  exports["voidCallbackWithData"] =
+      Function::New<VoidCallbackWithData>(env, nullptr, &testData);
+  exports["valueCallbackWithData"] =
+      Function::New<ValueCallbackWithData>(env, nullptr, &testData);
+  exports["callWithArgs"] = Function::New<CallWithArgs>(env);
+  exports["callWithVector"] = Function::New<CallWithVector>(env);
+  exports["callWithReceiverAndArgs"] =
+      Function::New<CallWithReceiverAndArgs>(env);
+  exports["callWithReceiverAndVector"] =
+      Function::New<CallWithReceiverAndVector>(env);
+  exports["callWithInvalidReceiver"] =
+      Function::New<CallWithInvalidReceiver>(env);
+  exports["callConstructorWithArgs"] =
+      Function::New<CallConstructorWithArgs>(env);
+  exports["callConstructorWithVector"] =
+      Function::New<CallConstructorWithVector>(env);
+  exports["isConstructCall"] = Function::New<IsConstructCall>(env);
+  result["templated"] = exports;
+  return result;
 }
diff --git a/test/function.js b/test/function.js
@@ -2,15 +2,17 @@
 const buildType = process.config.target_defaults.default_configuration;
 const assert = require('assert');
 
-test(require(`./build/${buildType}/binding.node`));
-test(require(`./build/${buildType}/binding_noexcept.node`));
+test(require(`./build/${buildType}/binding.node`).function.plain);
+test(require(`./build/${buildType}/binding_noexcept.node`).function.plain);
+test(require(`./build/${buildType}/binding.node`).function.templated);
+test(require(`./build/${buildType}/binding_noexcept.node`).function.templated);
 
 function test(binding) {
   let obj = {};
-  assert.deepStrictEqual(binding.function.voidCallback(obj), undefined);
+  assert.deepStrictEqual(binding.voidCallback(obj), undefined);
   assert.deepStrictEqual(obj, { "foo": "bar" });
 
-  assert.deepStrictEqual(binding.function.valueCallback(), { "foo": "bar" });
+  assert.deepStrictEqual(binding.valueCallback(), { "foo": "bar" });
 
   let args = null;
   let ret = null;
@@ -25,50 +27,50 @@ function test(binding) {
   }
 
   ret = 4;
-  assert.equal(binding.function.callWithArgs(testFunction, 1, 2, 3), 4);
+  assert.equal(binding.callWithArgs(testFunction, 1, 2, 3), 4);
   assert.strictEqual(receiver, undefined);
   assert.deepStrictEqual(args, [ 1, 2, 3 ]);
 
   ret = 5;
-  assert.equal(binding.function.callWithVector(testFunction, 2, 3, 4), 5);
+  assert.equal(binding.callWithVector(testFunction, 2, 3, 4), 5);
   assert.strictEqual(receiver, undefined);
   assert.deepStrictEqual(args, [ 2, 3, 4 ]);
 
   ret = 6;
-  assert.equal(binding.function.callWithReceiverAndArgs(testFunction, obj, 3, 4, 5), 6);
+  assert.equal(binding.callWithReceiverAndArgs(testFunction, obj, 3, 4, 5), 6);
   assert.deepStrictEqual(receiver, obj);
   assert.deepStrictEqual(args, [ 3, 4, 5 ]);
 
   ret = 7;
-  assert.equal(binding.function.callWithReceiverAndVector(testFunction, obj, 4, 5, 6), 7);
+  assert.equal(binding.callWithReceiverAndVector(testFunction, obj, 4, 5, 6), 7);
   assert.deepStrictEqual(receiver, obj);
   assert.deepStrictEqual(args, [ 4, 5, 6 ]);
 
   assert.throws(() => {
-    binding.function.callWithInvalidReceiver();
+    binding.callWithInvalidReceiver();
   }, /Invalid (pointer passed as )?argument/);
 
-  obj = binding.function.callConstructorWithArgs(testConstructor, 5, 6, 7);
+  obj = binding.callConstructorWithArgs(testConstructor, 5, 6, 7);
   assert(obj instanceof testConstructor);
   assert.deepStrictEqual(args, [ 5, 6, 7 ]);
 
-  obj = binding.function.callConstructorWithVector(testConstructor, 6, 7, 8);
+  obj = binding.callConstructorWithVector(testConstructor, 6, 7, 8);
   assert(obj instanceof testConstructor);
   assert.deepStrictEqual(args, [ 6, 7, 8 ]);
 
   obj = {};
-  assert.deepStrictEqual(binding.function.voidCallbackWithData(obj), undefined);
+  assert.deepStrictEqual(binding.voidCallbackWithData(obj), undefined);
   assert.deepStrictEqual(obj, { "foo": "bar", "data": 1 });
 
-  assert.deepStrictEqual(binding.function.valueCallbackWithData(), { "foo": "bar", "data": 1 });
+  assert.deepStrictEqual(binding.valueCallbackWithData(), { "foo": "bar", "data": 1 });
 
-  assert.equal(binding.function.voidCallback.name, 'voidCallback');
-  assert.equal(binding.function.valueCallback.name, 'valueCallback');
+  assert.equal(binding.voidCallback.name, 'voidCallback');
+  assert.equal(binding.valueCallback.name, 'valueCallback');
 
   let testConstructCall = undefined;
-  binding.function.isConstructCall((result) => { testConstructCall = result; });
+  binding.isConstructCall((result) => { testConstructCall = result; });
   assert.ok(!testConstructCall);
-  new binding.function.isConstructCall((result) => { testConstructCall = result; });
+  new binding.isConstructCall((result) => { testConstructCall = result; });
   assert.ok(testConstructCall);
 
   // TODO: Function::MakeCallback tests