From: "John Lam (DLR)" <jflam@...>
Date: 2007-10-24T02:38:49+09:00
Subject: OT: Is C# just Java renamed? WAS: IronRuby...will it be like J++?

Phlip [mailto:phlip2005@gmail.com]:

> C# is really Java with some of the keywords
> searched-and-replaced. And the license terms rewritten.

Since I don't think that most folks on this list are tracking what's happening in C#, and that many folks appreciate beautiful code, here's something that I hacked up in the latest version of C# (3.0) that we're shipping by the end of the year (betas of this are currently available).

These are extension methods, which is a static form of monkey patching. Here we're adding the SelectCustomAttributes<T> generic method to both Type and MethodInfo:

static class ExtensionMethods {
    public static IEnumerable<T> SelectCustomAttributes<T>(this Type type) where T : Attribute {
        return type.GetCustomAttributes(typeof(T), false).Cast<T>();
    }

    public static IEnumerable<T> SelectCustomAttributes<T>(this MethodInfo method) where T : Attribute {
        return method.GetCustomAttributes(typeof(T), false).Cast<T>();
    }
}

Here's a LINQ query that uses the Reflection APIs (not modified at all to support LINQ) to retrieve all of the methods on type t that are marked with the RubyMethodAttributecustom attribute. Note the call to the extension method SelectCustomAttributes on the MethodInfo object returned from t.GetMethods().

Type t = GetTypeFromSomewhere();
var methods = (from m in t.GetMethods()
               where m.IsDefined(typeof(RubyMethodAttribute), false)
               select m.SelectCustomAttributes<RubyMethodAttribute>().First());

Note the use of the var keyword to infer the type of custom attributes (pretty obvious here, but sure beats typing it) from the query.

This code is part of a little utility that I wrote in IronRuby to determine how many methods that we have implemented in our libraries. Once I get SVN unwedged after my adventures yesterday you can grab that code to take a closer look.

Scott Hanselman also posted a version of my utility on his blog: http://www.hanselman.com/blog/TheWeeklySourceCode8.aspx

BTW, I'm fairly certain that you can't do this in Java today, but I could be mistaken.

-John