C++/CX generic <class T> delegate

Question

Hi,

Please help C# developers to pitch in to C++/CX.

According to MSDN

http://msdn.microsoft.com/en-us/library/windows/apps/hh755798.aspx

Generic delegates          

The declaration of a public generic delegate is emitted into metadata, and can then be specialized and instantiated by consuming code. This example declares a generic delegate:

C++

Copy

generic <typename T>
delegate void  MyEventHandler(T p1, T p2);

And that is it, about Generic delegates, period!!! Where is the code snippet?

I am stuck with compilation error:

Generator<StartEventArgs^>^ generator = () -> StartEventArgs^ { return ref new StartEventArgs(); };

#include <iostream>
using namespace std;

using namespace Platform;
using namespace Windows::Foundation;

generic <class T> delegate void  Generator();

ref class StartEventArgs sealed
{

};

ref class BuyNow sealed
{
	internal:
	event EventHandler<StartEventArgs^>^ Start;
	void OnStart();	 
};

void BuyNow::OnStart()
{
	auto func = [] () -> StartEventArgs^ { return ref new StartEventArgs(); };
	//Generator<StartEventArgs^>^ generator = () -> StartEventArgs^ { return ref new StartEventArgs(); };
	Platform::Details::Console::WriteLine("Not Fine!");
}

int main(Platform::Array<Platform::String^>^ args)
{	
	BuyNow^ bn = ref new BuyNow();
	bn->OnStart();	
	std::cin.get(); 
	return 0;
}

Here's the corresponding C# Code Snippet that works fine:

using System;

public sealed class StartEventArgs
{

}

class BuyNow
{
    public event EventHandler<StartEventArgs> Start;

    private delegate T Generator<T>();

    public void OnStart()
    {
        Generator<StartEventArgs> generator = () => { return new StartEventArgs(); };
        //Generator<StartEventArgs> generator = delegate { return new StartEventArgs(); };
        Console.WriteLine("Fine!");
    }    
}

class Program
{
    public static void Main()
    {
        BuyNow bn = new BuyNow();
        bn.OnStart();
        Console.ReadKey();
    }
}

Please help.

Thanks

Answer 1

Try using this:

generic <class T>
delegate T Generator();

and this:

	auto generator = ref new Generator<StartEventArgs^>( [] ()
    {
        return ref new StartEventArgs();
    });

Answer 2

Try using this:

generic <class T>
delegate T Generator();

and this:

	auto generator = ref new Generator<StartEventArgs^>( [] ()
    {
        return ref new StartEventArgs();
    });

Thanks for the answer, jrboddie.

Answer 3

Are you developing a Windows Store app?  Your use of main(), Console and std::cin, look strange to me in that context.

Start from a template for Windows Store apps.

Answer 4

Are you developing a Windows Store app?  Your use of main(), Console and std::cin, look strange to me in that context.

Start from a template for Windows Store apps.

Thanks for the reply, jrboddie. That was just for code snippet using CxxWinRTTemplate for illustrating. Actually I am a .NET developer pitching into C++/CX (and learning). Since, MSDN does not have elaborate syntax or code snippets for generic delegates (http://msdn.microsoft.com/en-us/library/windows/apps/hh755798.aspx), I use CxxWinRTTemplate (http://visualstudiogallery.msdn.microsoft.com/8116acc4-747b-4330-bfd1-fce04d798f4a) to understand C++/CX  syntax using a console application.

You code snippet works fine. Mea culpa.

Answer 5

Try using this:

generic <class T>
delegate T Generator();

and this:

	auto generator = ref new Generator<StartEventArgs^>( [] ()
    {
        return ref new StartEventArgs();
    });

What about classes with constructor overload?

For example:

Generator<AuthEventArgs^>^ generator =
 ref new Generator<AuthEventArgs^>
 (
 [&] ()
  {
             
    ref new AuthEventArgs(token);
  }
 );
}

I got this error:

Warning 1 warning C4570: 'Generator' : is not explicitly declared as abstract but has abstract functions C:\Users\rsomaskandan\Documents\Visual Studio 2012\Projects\CxxWinRTTemplate1\CxxWinRTTemplate1\RefTemplate.cpp 10 1 CxxWinRTTemplate1
Error 2 error C2440: 'return' : cannot convert from 'void' to 'AuthEventArgs ^' C:\Program Files (x86)\Microsoft Visual Studio 11.0\VC\include\vccorlib.h 850 1 CxxWinRTTemplate1

Here's the complete code snippet for you:

// RefTemplate.cpp : Defines the entry point for the console application.
//

#include <iostream>
using namespace std;
using namespace Platform;
using namespace Windows::Foundation;

generic <class T>
delegate T Generator();

		enum class ErrorType
		{
			UNKNOWN = 0,
			HTTP = 1,
			API = 2,
			NETWORK = 3
		};

		ref class StartEventArgs sealed
		{

		};

		ref class AuthEventArgs sealed
		{		
			private:
				String^ authEventArgsToken;

			public:
				AuthEventArgs(String^ token)
				{
					Token = token;
				}
				property String^ Token
				{
					String^ get()
					{
						return authEventArgsToken;
					}
					void set(String^ value)
					{
						authEventArgsToken = value;
					}
				}
		};

		ref class CancelEventArgs sealed
		{		
			private:
				String^ cancelEventArgsToken;

			public:
				CancelEventArgs(String^ token)
				{
					Token = token;
				}
				property String^ Token
				{
					String^ get()
					{
						return cancelEventArgsToken;
					}
					void set(String^ value)
					{
						cancelEventArgsToken = value;
					}
				}
		};

		ref class ErrorEventArgs sealed
		{		
			private:
				ErrorType errorEventArgsType;
				String^ errorEventArgsCode;
				String^ errorEventArgsMessage;
				String^ errorEventArgsDetail;

			public:
				ErrorEventArgs(String^ name, String^ message, String^ detail)
				{					
					 Code = name;
					 Message = message;
					 Detail = detail;
				}

				property String^ Code
				{
					String^ get()
					{
						return errorEventArgsCode;
					}
					void set(String^ value)
					{
						errorEventArgsCode = value;
					}
				}

				property String^ Message
				{
					String^ get()
					{
						return errorEventArgsMessage;
					}
					void set(String^ value)
					{
						errorEventArgsMessage = value;
					}
				}

				property String^ Detail
				{
					String^ get()
					{
						return errorEventArgsDetail;
					}
					void set(String^ value)
					{
						errorEventArgsDetail = value;
					}
				}
		};

		ref class CompleteEventArgs sealed
		{		
			private:
				String^ errorEventArgsToken;
				String^ errorEventArgsTransactionID;
				String^ errorEventArgsPayerID;

			public:
				CompleteEventArgs(String^ token, String^ transactionID, String^ payerID)
				{
					 Token = token;
					 TransactionID = transactionID;
					 PayerID = payerID;
				}
				property String^ Token
				{
					String^ get()
					{
						return errorEventArgsToken;
					}
					void set(String^ value)
					{
						errorEventArgsToken = value;
					}
				}

				property String^ TransactionID
				{
					String^ get()
					{
						return errorEventArgsTransactionID;
					}
					void set(String^ value)
					{
						errorEventArgsTransactionID = value;
					}
				}

				property String^ PayerID
				{
					String^ get()
					{
						return errorEventArgsPayerID;
					}
					void set(String^ value)
					{
						errorEventArgsPayerID = value;
					}
				}				
		};

ref class BuyNow sealed
{
	internal:
	event EventHandler<StartEventArgs^>^ Start;
	void OnStart();	 
	void OnAuth(String^ token);
	void OnCancel(String^ token);
	void OnError(String^ name, String^message);
	void OnError(String^ name, String^ message, String^ detail);
	void OnComplete(String^ token, String^ transactionId, String^payerId);
};

void BuyNow::OnStart()
{
	Generator<StartEventArgs^>^ generator = ref new Generator<StartEventArgs^>( [] ()
    {
        return ref new StartEventArgs();
    });
}

void BuyNow::OnAuth(String^ token)
{
Generator<AuthEventArgs^>^ generator = 
	ref new Generator<AuthEventArgs^>
	(
	[&] ()
		{
													
				ref new AuthEventArgs(token);
		}
	);
}

void BuyNow::OnCancel(String^ token)
{
	Generator<CancelEventArgs^>^ generator = ref new Generator<CancelEventArgs^>
											(
											[&] ()
												{
													
													 ref new CancelEventArgs(token);
												}
											);
}

void BuyNow::OnError(String^ name, String^message)
{					
	OnError(name, message, nullptr);
}

void BuyNow::OnError(String^ name, String^ message, String^ detail)
{
	Generator<ErrorEventArgs^>^ generator = ref new Generator<ErrorEventArgs^>
											(
											[&] ()
												{
													
													  ref new ErrorEventArgs(name, message, detail);
												}
											);		
	//Emit<ErrorEventArgs>(generator);
}

void BuyNow::OnComplete(String^ token, String^ transactionId, String^payerId)
{
	Generator<CompleteEventArgs^>^ generator = ref new Generator<CompleteEventArgs^>
											(
											[&] ()
												{
													
													 ref new CompleteEventArgs(token, transactionId, payerId);
												}
											);

	//EmitAndComplete<CompleteEventArgs>(generator);
}


int main(Platform::Array<Platform::String^>^ args)
{	
	BuyNow^ bn = ref new BuyNow();
	bn->OnStart();	
	std::cin.get(); 
	return 0;
}

I am a .NET developer pitching into C++/CX (and learning). Please help with Lamda expression syntax/code snippet illustration in C++/CX as MSDN documentation didn't help.

Thanks