Read or Write

Did you notice that the syntax diagram on page 243 shows both the get and set accessors as optional? You must have at least one accessor, but you don’t have to have them both. A property that has only a get accessor is called READ-ONLY, while a property that has only a set accessor is a WRITE-ONLY property.

Read-only properties are quite common. For the sake of efficiency, some properties of a type may be immutable; they cannot be changed once the object is created because doing so would be slower than creating a new object. Other properties are the result of a calculation. The area of a rectangle, for example, is the product of its length and width. It makes sense to expose Rectangle.Area, but if you allowed users to change the value, how would the system calculate the Length and Width properties? In situations like that, it makes sense for Area to be read-only.