How can I refactor our the type parameter from this code?

Question

I want to write an extension method that tests if an attribute is applied on a method call, and I'd like to specify the method as a lambda expression. Currently, I have the following (working) approach, but I really don't like the way this code looks:

// Signature of my extension method:
public static bool HasAttribute<TAttribute, TDelegate>(this Expression<TDelegate> method)

// Usage (current code)
Expression<Func<AccountController, LogInModel, string, ActionResult>> mut = (c, m, s) => c.LogIn(m, s);
mut.HasAttribute<ExportModelStateAttribute, Func<AccountController, LogInModel, string, ActionResult>>().ShouldBeTrue();

As you can see, I have to specify the delegate type twice, and neither time does it look pretty... I'd like to have something more like

// Usage (if I had my way...)
var mut = (c, m, s) => c.LogIn(m, s);
mut.HasAttribute<ExportModelStateAttribute>().ShouldBeTrue();

but I realize that might be asking a tad bit too much.

Is there any way I could refactor away the type arguments from my current code?

The reason I have the TDelegate type argument there in the first place, is that I want to use this regardless of method signature and return type, and depending on the number of input arguments and whether the method in question is a void or a function, TDelegate needs to vary. I don't want to have one different implementation for each number of input arguments to the method I test...

Update:
As Jay points out in a comment, I apparently don't need to specify the TDelegate type argument in the call to HasAttribute<>. The code now looks like this:

Expression<Func<AccountController, LogInModel, string, ActionResult>> mut = (c, m, s) => c.LogIn(m, s);
mut.HasAttribute<ExportModelStateAttribute>().ShouldBeTrue();

It's much better, but I still think the first line is pretty messy. Could it be even better?

Answer 1

The one thing you can do is replace the long ugly Func<AccountController, LogInModel, string, ActionResult> with

public delegate ActionResult myDelegate(AccountController accountController, LogInModel logInModel, string varString);

Expression<myDelegate> mut = (c, m, s) => c.LogIn(m, s);
mut.HasAttribute<ExportModelStateAttribute>().ShouldBeTrue();

Updated: to show example with the updated question. I do not think it can get much more simplifed.