The delegate signature looks like this:
protected delegate void Operation(ZMachine machine);
The array is intialized with a series of statements like this:
op[0] = op[32] = op[64] = op[96] = op[192] = z => z.Op0();
op[1] = op[33] = op[65] = op[97] = op[193] = z => z.Op1();
...
op[254] = z => z.Op254();
op[255] = z => z.Op255();
I was forced to create a wrapper method which allows the delegate (which is static) to call an instance method specified at the time of invocation. This is because the actual operations are virtual to deal with the changing behavior of the various Z-machine versions. Using lambdas instead of named methods makes things look cleaner and involves a lot less typing, but always bugged me because of the extra method call needed for each instruction that is executed. I could find no better way though.
Today while reading through some documentation I discovered a way to do this without the wrapper represented by the lambda. About a third of the way down the page I found this:
"When a delegate represents an open instance method, it stores a reference to the method's entry point. The delegate signature must include the hidden this parameter in its formal parameter list; in this case, the delegate does not have a reference to a target object, and a target object must be supplied when the delegate is invoked."
I'd never heard of open instance delegates before. This was exactly what I was looking for!
Now I can write a method like:
private static Operation CreateOperation(string method)
{
return (Operation)Delegate.CreateDelegate(typeof(Operation), typeof(ZmachineV1).GetMethod(method, BindingFlags.NonPublic BindingFlags.Instance));
}
and my array initialization looks like:
op[0] = op[32] = op[64] = op[96] = op[192] = CreateOperation("Operation0");
op[1] = op[33] = op[65] = op[97] = op[193] = CreateOperation("Operation1");
...
op[254] = CreateOperation("Operation254");
op[255] = CreateOperation("Operation255");
This reduces the size of the binary and removes the extra method call when each instruction is executed. I only wish C# had some sort of native support for this type of delegate, as the CreateOperation method is ugly and can fail at runtime if the wrong name is passed whereas delegate creation using a method group name is checked at compile time.
I've nearly finished my refactoring and hope to make some code publicly available soon.
[Update: Thanks for the comments. They inspired me to keep trying.]
I'll admit I'm inexperienced with functional programming. It gives me headaches.
From what I see, expression trees reintroduce the code bloat I had with the lambdas. Honestly I didn't look into it deep enough to see if the extra method call gets reinserted at execution time.
Anyway, I played around with it some more and came up with this (sorry about the formatting):
namespace ConsoleApplication1
{
using System;
///
/// The program.
///
internal class Program
{
///
/// Program entry.
///
private static void Main()
{
var z = new ZmachineV2();
z.Run();
}
///
/// The zmachine V1.
///
private class ZmachineV1
{
///
/// The operations.
///
private static Operation[] operations;
///
/// A fake op (Needed to get the MethodInfo).
///
private delegate void FakeOp();
///
/// An operation.
///
///
/// The zmachine.
///
private delegate void Operation(ZmachineV1 zmachine);
///
/// Gets the operations.
///
///
/// The operations.
///
private Operation[] Operations
{
get
{
return operations ?? (operations = this.InitializeOperations());
}
}
///
/// Runs one cycle of the zmachine.
///
public void Run()
{
this.Operations[0](this);
}
///
/// Operation 0.
///
protected virtual void Operation0()
{
Console.WriteLine("Called ZmachineV1.Operation0.");
}
///
/// Creates an operation.
///
///
/// The fake operation.
///
///
/// An operation.
///
private static Operation CreateOperation(FakeOp fake)
{
return (Operation)Delegate.CreateDelegate(typeof(Operation), fake.Method.GetBaseDefinition());
}
///
/// Initializes the operations.
///
///
/// The operations.
///
private Operation[] InitializeOperations()
{
var ops = new Operation[1];
ops[0] = CreateOperation(this.Operation0);
return ops;
}
}
///
/// The zmachine V2.
///
private class ZmachineV2 : ZmachineV1
{
///
/// Operation 0.
///
protected override void Operation0()
{
Console.WriteLine("Called ZmachineV2.Operation0.");
}
}
}
}
The only downsides to this that I see are that I had to give up the readonly modifier on the delegate array, wrap it in a property, create another delegate type, and the initialization generates a bit of garbage for the FakeOp delegates. On the plus side, the CreateOperation method looks better and I no longer need to refer to anything in the Reflection namespace, so I can drop the using statement for that. I no longer need to pass strings and my method names are verified at compile time. I also don't need any wrapper methods. What do you think?
