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

A readonly variable is very much like const in that the value is constant throughout its lifetime. The difference is that a readonly variable is initialized at run-time and const is at compile time. Static, in sort of laymen terms, means that the instance of the variable does not depend on the instance of the object it is declared in. Its lifetime persists from function call to function call. A static variable is faster to access because its storage remains allocated for the entire duration of the program. So knowing this we can go back to your question.

Why is 'logger' a static member? That's a design decision. I need to know how you're using it to answer this question. Why is it readonly? Because it seems like it's initialized once and its instance is used throughout. We can make sure that nobody else tampers with the value of logger by making it 'read-only' right after we initialize it.