Call C++ generic instance method from .NET DLL

This article provides an introduction to cross-technology invocation of instance generic methods. Generic methods in C# (.NET) and Java technologies are methods that are declared with the type parameter in its signature, allowing it to be used with any data type. It is described in detail in article about generic methods in .NET and article about generic methods in Java.

Javonet allows you to reference and use modules or packages written in (Java/Kotlin/Groovy/Clojure, C#/VB.NET, Ruby, Perl, Python, JavaScript/TypeScript) like they were created in your technology. If have not yet created your first project check Javonet overview and quick start guides for your technology.

With Javonet you can interact with generic instance methods from .NET DLL like they were available in C++ but invocation must be performed through Javonet SDK API.

Javonet allows you to pass any C++ value type as argument to method from .NET DLL. For reference type arguments (instances of other classes) you can create such instance with Javonet and pass the Invocation Context variable referencing that object as argument of method invocation.

Custom .NET DLL with C++ generic methods

With Javonet it is possible to reference any custom .NET DLL and interact with its methods declared on types defined within that module almost the same as with any other C++ library.

Snippet below represents the sample code from .NET DLL which contains generic methods.

public static string GenericSampleStaticMethod<T>(T x, T y)
{
	return x + " and " + y;
}

public string GenericSampleMethod<T>(T x, T y)
{
	return x + " or " + y;
}

public K GenericSampleMethodWithTwoTypes<T, K>(T x)
{
	return default(K);
}

It is possible to invoke the declared methods from .NET DLL using following C++ code:

I code in:
// use Activate only once in your app
Javonet::Activate("your-license-key");

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Netcore();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.dll";
auto className = "TestClass.TestClass";

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance()->Execute();

// get type for generic method
auto targetType = calledRuntime->GetType("System.Int32");

// invoke instance generic method
auto response = instance->
	InvokeGenericMethod("GenericSampleMethod", { targetType, 7, 5 })->
	Execute();

// get value from response
auto result = std::any_cast<std::string>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This snippet uses in memory runtime bridging to load the .NET DLL.
Next, type is specified and instance of class is created.
Next, generic instance method is invoked.
While calling .NET generic method it is necessary to pass method name, type and arguments.
While calling Java generic method it is necessary to pass method name and arguments.

To invoke method which has more than one type specified:

I code in:
// use Activate only once in your app
Javonet::Activate("your-license-key");

// create called runtime context
auto calledRuntime = Javonet::InMemory()->Netcore();

// set up variables
auto libraryPath = resourcesDirectory + "/TestClass.dll";
auto className = "TestClass.TestClass";

// load custom library
calledRuntime->LoadLibrary(libraryPath);

// get type from the runtime
auto calledRuntimeType = calledRuntime->GetType(className)->Execute();

// create type's instance
auto instance = calledRuntimeType->CreateInstance()->Execute();

// get types for generic method
auto targetType1 = calledRuntime->GetType("System.String")->Execute();
auto targetType2 = calledRuntime->GetType("System.Int32")->Execute();

// invoke type's generic method
auto response = instance->
	InvokeGenericMethod("GenericSampleMethodWithTwoTypes",
		{ std::vector<std::any>{ targetType1, targetType2 },
						  "test" })->Execute();

// get value from response
auto result = std::any_cast<int>(response->GetValue());

// write result to console
std::cout << result << std::endl;

This snippet uses in memory runtime bridging to load the .NET DLL.
Next, type is specified and instance of class is created.
Next, generic instance method is invoked.
While calling .NET generic method it is necessary to pass method name, type and arguments.
While calling Java generic method it is necessary to pass method name and arguments.
The same operation can be performed remotely by just changing the new Runtime Context invocation from in memory to tcp that will create and interact with your .NET DLL objects on any remote node, container or service that hosts Javonet Code Gateway. This way you can preserve the same logic in your application and instantly switch between monolithic and microservices architecture without the need to implement the integration layer based on web services or other remote invocation methods.

Read more about use cases and software architecture scenarios where Javonet runtime bridging technology can support your development process.

Additional references