Covariance and Contravariance in C#, Part Three: Method Group Conversion Variance

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, so let me spell it out in more detail. Suppose…

14

Covariance and Contravariance in C#, Part Two: Array Covariance

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, and “make an array of” is a covariant operation on types, Giraffe[] is smaller than…

20

Covariance and Contravariance in C#, Part One

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 3.0 already support today, and then discuss some ideas we are…

23