Follow up for the second c#ID Study Group Meeting

Very good discussion arround generics. It is baffling how you gain insight when trying to explain something.

I've found that most developers don't now the concept of single, double and multiple dispatch.
I strongly recomment to read up on this:

• Multiple Dispatch
• Visitor Pattern
  

Preparation for the second meeting of the c#ID Study Group Würzburg

The last meeting has been quite a long time ago because one of us three took a vacation of a couple of weeks. So here we are back again.

The topic of this meeting is chapter 3: Parameterized typing with generics.

As I am now in my 4th year of developing with C# 2 there have been few really new and stunning facts in this chapter. Still I’ve learned quit a good bit and I was able to pick up quite a couple of terms that help me clarify my understanding of how generics work.

Here are the main points that were very valuable to me:

• The diagram on page 68 is really an eye opener as it explains the relationship between unbound generic types, constructed (generic) types and instances. I wont put a copy of this diagram here. Go get the book!
• The way the runtime constructs a type from an unbound generic type for each different combination of the generic parameters.
• The way comparison are performed with the == and != operators based on the constraints on the generic type parameters as explained on pp 82, 83.
• Very interesting is the demonstration on page 87 that each constructed type has its own static constructor .
• I cannot remember finding any hint, that there are no generic methods in C++. Which is obvious if you look at how templates are a king of "preprocessor on steroids". The generic parameters of generic methods are only available at runtime (are they really?) but not at compile time.
  Which leads me to another question: Are generic parameters of methods resolved based on the runtime or on the compile time type?
• OMG: Covariance and Contravariance again!
• On p. 103 the options for working arround the invariance of generic types. The last item talks about a generic helper method to convert the items in a collection. Here should be mentioned that there is a method System.Linq.Enumerable.Cast(IEnumberable) that does just that. I think a hint would be in order even if this C# 3 features are dealt with later in the book.