As I discussed last time, were we to introduce interface and delegate variance in a hypothetical future version of C# we would need a syntax for it. Here are some possibilities that immediately come to mind. Option 1: interface IFoo<+T, -U>...

Suppose we were to implement generic interface and delegate variance in a hypothetical future version of C#. What, hypothetically, would the syntax look like? There are a bunch of options that we could hypothetically consider. Before I get into options...

Over the last few posts I’ve discussed how it is possible to treat a delegate as contravariant in its arguments and covariant in its return type. A delegate is basically just an object which represents a single function call; we can do this same kind...

Last time I discussed how we could in a hypothetical future version of C# allow delegate types to be covariant in their return type and contravariant in their formal parameter types. For example, we could have a contravariant action delegate: delegate...

In the last two posts I discussed the two kinds of variance that C# already has -- array covariance and member-group-to-delegate conversion covariance (on return types) and contravariance (on formal parameter types). Today I want to generalize the...

Last time I discussed how array covariance is broken in C# (and Java, and a number of other languages as well.) Today, a non-broken kind of variance supported by C# 2.0: conversions from method groups to delegates. This is a more complicated kind of variance...

C# implements variance in two ways. Today, the broken way. Ever since C# 1.0, arrays where the element type is a reference type are covariant . This is perfectly legal: Animal[] animals = new Giraffe[10]; Since Giraffe is smaller than Animal...

I have been wanting for a long time to do a series of articles about covariance and contravariance (which I will shorten to “variance” for the rest of this series.) I’ll start by defining some terms, then describe what variance features C# 2.0 and...

The other morning I got the following question from a reader: I have created a client-server application in C# using asynchronous socket methods [... blah blah blah, a long description of a scenario in which the socket misses packets under certain...

Finally we are ready to translate our pseudocode into C# 3.0. What do we need to make the algorithm run? We need a start node, a destination node, a function which tells us the exact distance between two neighbours, and a function which tells us the...

In order to make the A* algorithm work we need to get the lowest-estimated-cost-path-discovered-so-far out of the list of paths under consideration. The standard data structure for doing so is called a “priority queue”. Priority queues are so-called because...

In order to implement the A* algorithm in C# 3.0 I am going to need to implement some custom data structures. Today we’ll consider how to implement the “path”. You’ll notice in my description of the algorithm that the only operations we perform on...

As we get into the home stretch for the Orcas release I’ve been spending a little time lately just playing around implementing some “classic” algorithms and data structures in C#. The one I implemented today is the famous A* algorithm. Surely you’ve...