Chapter 4

1. A class is a template or a blueprint that specifies the form of an object. It contains both data and code that operates on that data. An object is an instance of a class. A class is introduced with the class keyword and defines a reference type. A structure is introduced with the struct keyword and defines a value type. Unlike classes, structures do not support inheritance and cannot have an explicit default constructor, and fields cannot be initialized during declaration unless they are declared const or static.
2. A read-only field is a field defined with the readonly specifier. Such a field can only be initialized in a constructor and its value cannot be changed later.
3. Expression body definitions are an alternative syntax, typically for methods and properties, that simply consist of evaluating an expression and perhaps returning the result of the evaluation. These have the form member => expression. They are supported for all class members, not just methods...