The ideas and concepts that the Microsoft research team has realized in spec# are too great not to be included in a future version of C# !

Just look a this example:

public static int Subtract(int x, int y)
     requires x > y;
     ensures result > y;
     return x - y;

It is not only the runtime aspects of spec# that are exiting. It is the amazing level of static analysis that they have implemented that at compile time validates (across many method boundaries) that requirements are uphold.

C# has really evolved a lot in the last two iterations (especially in 3.0), and think this fast evolution has given it a good edge compared to other static languages (java). But why stop now? Here are a few more things I would like in C# 4.0 :)

Extensible compilation pipeline:

The Boo .NET language has this concept of an extensible compilation pipeline that allows for really powerful usage scenarios. With it you can extend the language with new keyword constructs and attributes that actually manipulate the abstract syntax tree (AST). Here is an example where I have extended Boo with some constructs for design by contract:

[ensures(total > 0)] 
def Add(int value):
    requires value > 0
    total += value

Extending the Boo language like this is very trivial. For example the requires keyword is implemented like this:

macro requires:
  return [|
    if $(requires.Arguments[0]) == false:
        raise ArgumentException("requires precondition failed")

This is just a simple example, you can do more powerful stuff. A Boo macro is very different from C++ macros. The Boo macros operate on the compiler's AST and can query the object model and modify it in very powerful ways. The open compiler architecture makes Boo a language suitable for writing domain specific languages. I doubt that something like this will be implemented in C# though since new compiler features are more likely to break existing implementations. Something I think the C# team are not allowed to do.

Dynamic method invocation and duck typing:

If a class implements the IQuackFu interface in Boo you can call methods on it that are resolved at runtime. This is similar to method missing in ruby. The IQuackFu interface looks like this:

public interface IQuackFu
  object QuackGet(string name, object[] parameters);
  object QuackSet(string name, object[] parameters, object value);
  object QuackInvoke(string name, params object[] args);

This interface can for example be used as front to an xml document, allowing you to access elements as properties. I think the C# team is actually considering something like this if you are to believe the rumours from the MVP Summit.

Anyone else having ideas or a whish list for C# 4.0?