Is there a way to determine whether a parameter has this modifier?

Question

I would like to determine if a parameter has this modifier using Reflection.I have looked at properties of ParameterInfo class, but couldn't find anything useful.I know the extension methods are just syntactic sugars but I believe there should be a way to determine whether a method is an extension method.

The only thing that distinguishes extension methods from other static methods (that are defined in a static, public class) is this modifier.

For example this is not an extension method:

public static int Square(int x) { return x * x; }

But this is:

public static int Square(this int x) { return x * x; }

So how can I distinguish between two methods using Reflection or something else if possible?

Answer 1

It's not exactly the same, but you can check whether the method has the ExtensionAttribute applied to it.

var method = type.GetMethod("Square");
if (method.IsDefined(typeof(ExtensionAttribute), false))
{
    // Yup, it's an extension method
}

Now I say it's not exactly the same, because you could have written:

[Extension]
public static int Square(int x) { return x * x; }

... and the compiler would still pick it up as an extension method. So this does detect whether it's an extension method (assuming it's in a static top-level non-generic type) but it doesn't detect for certain whether the source code had the this modifier on the first parameter.