A very common IV question.
Diff #1) compile-time constants
Diff #2) ctor
http://msdn.microsoft.com/en-us/library/acdd6hb7(v=vs.71).aspx shows you can set a readonly field in an initializer and again in
ctor. Usage — you can set a default-default by initializer, use it in ctor, and change its value at end of ctor.