C# Features As Requested By Others: Please No Duck Type By Default in C#

I replied to a blog post by Tosos over here:

The reply was long enough that I thought it warranted posting here too. I expand on why “var” is not dangerous and can go away. I also describe why it isn’t duck or dynamic or anything but strong and static. If you know F# this is nothing new to you.

Here it is:

I love these.

@Mike Borozdin:
Consider F#’s definition of methods(functions). It is just as strongly typed as C#, yet the compiler is left to infer the return type.

In the example above the return type is not weak, it is not vague or dynamic or relying on duck typing. The return type is the anonymous type defined by the select clause of the linq statement. All of the static type checking and strength of warnings and errors of the compiler will still occur.

I’d like to see similar syntax, but drop the var, it is needless noise.


public GetFirstPageOfFiles(string dir)
  return Directory.GetFiles(dir).Take(10);

The signature of the method GetFiles takes a string and returns a string so we (and the compiler) KNOWS that GetFirstPageOfFiles returns a string.

But have we simplified the language as much as we can? F# wouldn’t make me specify the type of the argument to the method. It would infer it.

public GetFirstPageOfFiles(dir)
  return Directory.GetFiles(dir).Take(10);

Again, the argument to GetFiles is string so the compiler knows how to turn the method signature of

public GetFirstPageOfFiles(dir)


public string GetFirstPageOfFiles(string dir)

Where the compiler can’t infer, it should give an error and require the explicit use of the type.

This exactly the behavior of var now.

As for #3, I would NOT want this to be the default behavior. The default behavior should be strong-static types. As strong and as static as possible. That said, some compiler support for the equivalent of duct typing via reflection would be rather nice. AFAIK what you are asking for is already available through a 3rd party library from David Meyer at http://www.deftflux.net/blog/page/Duck-Typing-Project.aspx

With respect to default behavior being duck, Phil Haack is wrong, everyone is wrong. If you want that, use Iron Ruby or Iron Python.

I wrote about my uncertainty about the GetEnumerator duck here: http://jrwren.wrenfam.com/blog/2007/07/21/c-has-duck-typing/  It may have been necessary. If it wasn’t necessary, I’d call it a mistake. Maybe it was an accident. I don’t know.

Could I be more against duck typing? Yes, I could be against it entirely. I could completely misunderstand it. Unfortunately I’ve written in duck languages. I’ve probably written more code in PHP, Python and Perl than I have in C#. (I wrote A LOT of Perl and PHP.)

My simply request is to require the manual selection of behavior of duck, like Boo. Yes, I say “like boo” a lot, but much could be learned from boo. Boo had extension methods before C#. Boo has duck in a strong, static typed language. Of course, boo is not a special case. It is best to learn as much as possible from neighbors so that you can make your own decisions about things. My request is probably going to be granted. Charlie Calvert wrote about the dynamic keyword and dynamic blocks as a possible solution to this.

Business Logic is a Bad Word

I do not write business applications. Oh sure, I write applications for a business. This business makes money. The applications which I write helps them make more money. However, these applications are in the domain of product engineering. They are not in the domain of running the business. They do not deal with cash flow, inventory, accounts receivable or payable. There is no letter opener of death involved with any of my application users.

My applications have no Business Logic. The business processes could change at this company and my applications don’t know anything about it. We solve engineering problems. That said, separation of UI and Business Logic is still a strong concern. It isn’t Business Logic. It is Application Logic.

Why mention this? I feel like there are programmers out there who say to themselves, “I do not write business applications, therefore this silly separation of business logic does not apply to me.” These programmers are wrong. Separation of application logic from UI code is valid not matter what the application. Separation of Concerns extends to every type of software. I cannot imagine a type of software from which separation of concerns does not benefit. I’ll go so far as to say that if you think you have a case: that you are wrong. If you think you can justify it to me, I will simply redesign to a case which does fit.

Do you write math apps?  Separate your Math Logic from your UI.

Do you write engineering apps? Separate your Engineering Logic from you UI.

Do you write medical apps? Separate your Medical Logic from your UI.

Do you write biology apps? Separate your Biology Logic from your UI.

Do you write Anthropology apps? Separate your Anthropology Logic from your UI.

Do you write Sociology apps? Separate your Sociology Logic from your UI.

Do you write Psychology apps? Separate your Psychology Logic from your UI.

Do you write Legal apps? Separate your Legal Logic from your UI.

Do you see a pattern here? Separate your seeing of patterns from your UI.  Good.

C# vNext feature request 2

I previously had a list of things I wanted. Yes, I am like a 2-year old. I want. I want. I want.

mdavey posted a link to a channel 9 video which made me rethink my request. Oh I still want all of the original list and… I want more. I want more. I want more.

  • List Literals – it is silly that I even have to request this
  • Dictionary Literals – see list literals for comments
  • Extensible Literals – the .NET BCL already has this really great type conversion system. You ask for a type converter for a specific type and whether or not it can be converted between two types. One of these types is often a string. You can write your own converters and register them with this system of type converters. It is very elegant and beautiful. The compiler should use this to let me express my own literals. Type initializers are nice, but this would be nicer.
  • Variable Generic Type Parameter ArityChris Marinos had a use case for this and had to implement a solution in a much less elegant way because he was missing this feature. Its a request in Java too. Cliff Biffle says that Mongoose has them, but I can’t find whatever became of the smalltalk inspired language.
  • Restricted Types – The same post on Variable Generic Type Parameter Arity, Cliff reminded me of my favorite Modula-3 feature. He points out that Dylan has it. I like Modula-3’s approach to this using Subtypes. This paper by Cardelli, Donahue, Jordan, Kalsow and Nelson does a great job of explaining Modula-3’s simple but powerful type system. Not all of the subtypes in M3 make sense in a .NET world. We already have a well defined type system and some of the constructs would not mix. One concept that I think would mix well is range subtypes. Imagine that you know a value is always going to be between zero and 100. You can define a subtype of int and use that type throughout your program. The compiler actually checks that variables of this type are never out of this predefined  range. Type Conversion is automatic from int subtype to int type, but not the other way. It is awesome if for nothing other than eliminating IndexOutOfRangeException on array indexers.


Yes, I do want my cake and to eat it too.

MVP For Me

A week ago, on Tuesday, July 1st, I received a strange email. I should have known it was going to be a strange day. I was wearing my Ohio Linux Fest 2006 t-shirt. I had just listened to Java Posse podcast and was listening to Mac Break Weekly. Since I don’t write java code and I don’t own a mac, I should have know I was playing with fate.

This email might have been a joke. It was short and to the point, exactly the opposite I would expect for an email of this subject matter. It should have been some crazy HTML formatted table of disgustingness which I would have initially dismissed as spam. It should have had embedded images and fancy fonts. It had none of these things.

The email subject said very simply and plainly, “Congratulations! you have received the Microsoft MVP Award”. Surely someone was playing a trick on me. It was probably one of my old Linux buddies making fun of me for using so much Microsoft software these days.

I opened the message to read, “Congratulations! We are pleased to present you with the 2008 Microsoft® MVP Award! The MVP Award is our way to say thank you for promoting the spirit of community and improving people’s lives and the industry’s success every day. We appreciate your extraordinary efforts in Visual C# technical communities during the past year….”

It looks legit. I don’t know what I did to deserve such an award, but I’m grateful for it. I plan on continuing doing whatever it I’ve been doing.

Who knew that an perl loving, linux loving, python loving, linux kernel hacking, mono loving, C# loving, boo loving, F# loving, wife loving baby loving insane hacker could be a C# MVP. I sure didn’t.

Thanks to anyone who put in a good word about me.