C# 4.0 Dynamic Lookup
I really like the way the C# team tackled bring dynamic programming to the language. C# is a static language but it is good to see that the C# team is pragmatic enough to realise that will always be situations where you don’t have type information at compile time.
With C# 4.0 rather than having to bust out ugly System.Reflection operations to interact with unknown objects, the new dynamic lookup hides any ugliness away from the developer. Statically typing an object as dynamic is a great solution as it lets you treat a specific object, which you don’t have type knowledge of, as you want with regular property and method calls while still keeping static typing throughout the rest of your application. I think this is a much better solution than the dynamic block discussed in the past.
Dynamic lookup also opens up some new interesting paradigms by offering the IDynamicObject interface to developers. The first thing I thought of when I saw it was Dynamic LINQ to JSON. I’m sure uses will come out of it that no one ever considered
C# 4.0 Covariance and Contravariance
Very happy to see this feature. I bumped my head into generic variance issues a number of times when writing LINQ to JSON. No longer having to worry about IEnumerable<JToken> not being compatible with IEnumerable<object> is great. They even kept it type safe!
C# 4.0 Named and optional parameters
Is it just me or did Anders wince when announcing named and optional parameter support in C# 4.0? Microsoft has said that they plan to keep the C#/VB.NET languages in sync and I wonder if this is C# inheriting VB.NET features by default.
.NET 4.0 Code Contracts
From everything I have seen of it so far I love the Code Contracts feature. Statically defining type information has been around forever and is A Good Thing. Its about time that we are able to statically define valid values as well.
.NET 4.0 Parallel Extensions
It is interesting to see parallel programming come as a library addition in the form of Parallel Extensions rather than a language feature (ditto for code contracts). I guess with a library you only need to create it once rather than having to figure out new concurrent programming syntax for every .NET language.
Bring on VS2010.