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The Data Type Class Hierarchy

It is very interesting to note that even the primitive .NET data types are arranged in a “class hierar-

chy.” If you are new to the world of inheritance, you will discover the full details in Chapter 6. Until

then, just understand that types at the top of a class hierarchy provide some default behaviors that

are granted to the derived types. The relationship between these core system types can be under-

stood as shown in Figure 3-6.

Figure 3-6.

The class hierarchy of system types

C H A P T E R   3  

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C O R E   C #   P R O G R A M M I N G   C O N S T R U C T S, PA RT   I

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Notice that each of these types ultimately derives from System.Object, which defines a set of

methods (ToString(), Equals(), GetHashCode(), and so forth) common to all types in the .NET base

class libraries (these methods are fully detailed in Chapter 6).

Also note that many numerical data types derive from a class named System.ValueType.

Descendents of ValueType are automatically allocated on the stack and therefore have a very pre-

dictable lifetime and are quite efficient. On the other hand, types that do not have System.ValueType

in their inheritance chain (such as System.Type, System.String, System.Array, System.Exception,

and System.Delegate) are not allocated on the stack, but on the garbage-collected heap.

Without getting too hung up on the details of System.Object and System.ValueType for the time

being (again, more details in Chapter 4), just understand that because a C# keyword (such as int) is

simply shorthand notation for the corresponding system type (in this case, System.Int32), the fol-

lowing is perfectly legal syntax, given that System.Int32 (the C# int) eventually derives from

System.Object, and therefore can invoke any of its public members, as illustrated by this additional

helper function:

static void ObjectFunctionality()

{

Console.WriteLine("=> System.Object Functionality:");