Lambda Generic Expression w/ Out Parameter

Question

I am trying to use expressions w/ lambda delegates to obtain the name of the calling method but it is not formatting it properly.

Here is what I have so far: Question is.. how do I get what I am to expect similar to foo.Method.Name for both lambda and regular methods?

So far, I have tried with and without expressions.. and get the same results.

< HandleAddedDevice >b__2d

    // **************************************************************************
    public delegate TResult TimerDelegateOut <T, out TResult>(out T foo);

    // **************************************************************************
    public static string GetName<T>(this Expression<T> expression) {
      var callExpression = expression.Body as MethodCallExpression;
      return callExpression != null ? callExpression.Method.Name : string.Empty;
    }

    // **************************************************************************
    public static Expression<TimerDelegateOut<T, TResult>> ToExpression<T, TResult>(this TimerDelegateOut<T, TResult> call) {
      var p1 = Expression.Parameter(typeof(T).MakeByRefType(), "value");
      MethodCallExpression methodCall = call.Target == null
          ? Expression.Call(call.Method, p1)
          : Expression.Call(Expression.Constant(call.Target), call.Method, p1);
      return Expression.Lambda<TimerDelegateOut<T, TResult>>(methodCall, p1);
    }

    // **************************************************************************
    public static Expression<Func<TResult>> ToExpression<TResult>(this Func<TResult> call) {
      MethodCallExpression methodCall = call.Target == null
        ? Expression.Call(call.Method)
        : Expression.Call(Expression.Constant(call.Target), call.Method);
      return Expression.Lambda<Func<TResult>>(methodCall);
    }

    // **************************************************************************
    public static TResult TimeFunction<T, TResult>(TimerDelegateOut<T, TResult> foo, out T bar) {
      try {
        var result = foo.ToExpression().Compile().Invoke(out bar);
        Console.WriteLine(foo.GetName());   // is OKAY
        return result;
      } catch (Exception) {
        bar = default(T);
        return default(TResult);
      }
    }

    // **************************************************************************
    public static TResult TimeFunction<TResult>(Func<TResult> foo) {
      try {
        var result = foo.ToExpression().Compile().Invoke();
        Console.WriteLine(foo.GetName());   // <-- prints "foo" ???  Not correct.
        return result;
      } catch (Exception) {
        bar = default(T);
        return default(TResult);
      }
    }

-------------
Result GetCamera_HWInfo(out Cam_HWInfo obj)
{
  obj = new Cam_HWInfo() { < fill container here > };
  return Result.cmrOk;
}


//------------
private void HandleAddedDevice() {
    ...

  Cam_HWInfo camHWInfo;
  Result result = Watchdog.TimeFunction(GetCamera_HWInfo, out camHWInfo);

    ...

  // Try this one.. I am also using.
  var connect = new Func<bool>(delegate {
    try {
      // ...
    } catch (Exception ex) {
      return false;
    }
    return true;
  });

  result = Watchdog.TimeFunction(connect);
}

//------------
// Assume OEP
static void Main(string[] args)
{
  HandleAddedDevice();
}

---

Here is a test driver I can show in a simple case of what I would expect. The 3x methods I need to support are:

1. Func<T, TR>()
2. Func<T, TR>(T foo)
3. Func<T, TR>(out T foo)

Example: Lambda expressions are nameless. It will show up something like < No Name>.

.Method.Name is correct, but since it is a sub-method of its Parent within the calling scope, it actually is registered on the stack, as follows:

< HandleAddedDevice >b__2d

I read here that I might need to make it an expression and then Expression.Compile() to convert it to an Action (or in my case Func)?

They said it may not be possible without a compiled expression here... Maybe this will help you to explain to me where my code is a bit off in what I am trying to do.

      class Program {
        public static class ReflectionUtility {
          public static string GetPropertyName<T>(Expression<Func<T>> expression) {
            MemberExpression body = (MemberExpression) expression.Body;
            return body.Member.Name;
          }
        }

        static void Main(string[] args) {
          Func<int, bool> lambda = i => i < 5;
          Func<int, bool> del = delegate(int i) { return i < 5; };

          // Create similar expression #1.
          Expression<Func<int, bool>> expr1 = i => i < 5;
          // Compile the expression tree into executable code.
          Func<int, bool> exprC1 = expr1.Compile();

          // Invoke the method and print the output.
          Console.WriteLine("lambda(4) = {0}   :  {1} ", lambda(4), lambda.Method.Name);
          Console.WriteLine("del   (4) = {0}   :  {1} ",    del(4), del.Method.Name);
          Console.WriteLine("expr1 (4) = {0}   :  {1} ", exprC1(4), exprC1.Method.Name);
          Console.WriteLine("          =           {0}", ReflectionUtility.GetPropertyName(() => lambda));
          Console.WriteLine("          =           {0}", ReflectionUtility.GetPropertyName(() => del));

          Console.Write("Press any key to continue...");
          Console.ReadKey();
        }

OUTPUT

lambda(4) = True   :  <Main>b__0
del   (4) = True   :  <Main>b__1
expr1 (4) = True   :  lambda_method
          =           lambda
          =           del
Press any key to continue...

Answer 1

I don't think it's possible. On Compiler Error CS1951 they write:

An expression tree just represents expressions as data structures. There is no way to represent specific memory locations as is required when you pass a parameter by reference.

Answer 2

It looks like everything is fine except for how you are trying to extract the method name. Try this:

public static string GetName<T>(Expression<T> field)
{
    var callExpression = field.Body as MethodCallExpression;
    return callExpression != null ? callExpression.Method.Name : string.Empty;
}