C# private, static, and readonly

Question

I was reviewing some code for log4net and I came across this.

private static readonly ILog logger = LogManager.GetLogger(typeof(AdminClient));

Answer 1

The reason to put a readonly flag on a private variable is to declare that the variable will always reference the same object. It's true that being private makes it invisible to anyone outside the class, but this way we can make sure we didn't accidentaly overwrite the variable with a new object, by writing something like

logger = LogManager.GetLogger(typeof(AdminClient));

somewhere else in our class. With readonly it just won't compile (Unless it was not initialized before, and we are in the (static) constructor)