CODEWITHSUNDEEP
c#delegatesdeclarationforward
iam
iam

Reputation: 1713

C# recursive delegate declaration problem

* PLEASE SEE END FOR IMPORTANT EDIT *

For various reasons I have something like:

delegate void Task(QueueTask queueTask); delegate void QueueTask(Task task);

Using Visual Studio Express 2008 this works more or less fine apart from in lambda expressions where it can't deduce if I try call and call queueTask() in the function without explicit help:

void MyTask(QueueTask queueTask)
{
   queueTask(qt => {}); // fails with queueTask doesn't take 1 parameter?
}

This works though:

void MyTask(QueueTask queueTask)
{
   queueTask((QueueTask qt) => {});
}

Its not a huge problem and I know I could also probably get away by passing in another object that contained the delegate instead but I was curious if there was a way to make it work as its stands?

Thanks.

* IMPORTANT EDIT BELOW *

It seems only if I put the class 'TaskPool2' in a separate assembly I get the compile error!?

namespace Test
{
    public class TaskPool2
    {
        public delegate void QueueTask(Task task);
        public delegate void Task(QueueTask queueTask);


        public void Queue(Task task) { }
    }
}


namespace MyApp
{
    class Program
    {
        static void SomeFunc()
        {
            Test.TaskPool2 taskPool = new Test.TaskPool2();


            taskPool.Queue(queue => { Console.WriteLine("A"); queue(q => Console.WriteLine("C")); });
        }
    }
}

Granted its somewhat convoluted!

Upvotes: 1

Views: 1578

Answers (2)

Neowizard
Neowizard

Reputation: 3017

After using several ways to break\fix the code, I've found a small bit of information.

When the compiler reaches the line 

taskPool.Queue(queue => { Console.WriteLine("A"); queue(q => Console.WriteLine("C")); });

it'll fall compilation if (and I think only if) it never encountered QueueTask before. For instance, declaring the next line in the class (before or after the SomeFunc method)

Public Delegate Test.TaskPool2.QueueTask x;

would fix the compilation. Also, adding the next line above the errornouse line will also fix it

Test.TaskPool2.QueueTask x; // declare x to be QueueTask

I've tried a few more lines using QueueTask, and they worked (fix the compilation).

I can only assume that the compiler doesn't load the definition for QueueTask, and this leads to this strangment.

Seems even like a bug.

Hope I managed to explain this well.

Upvotes: 1

Jon Skeet
Jon Skeet

Reputation: 1500515

(This would have been a comment, but it's not really feasible to give full code in comments.)

Your code already works as it stands:

delegate void Task(QueueTask queueTask);
delegate void QueueTask(Task task);

class Test
{
    void MyTask(QueueTask queueTask)
    {
        queueTask(qt => {}); // fails with queueTask doesn't take 1 parameter?
    }
}

Compiles with no problems.

Please create a similarly short but complete program which doesn't compile.

Upvotes: 0

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