#38 – Data Type Hierarchy

All types in .NET inherit from another type, except for System.Object (object), which is at the top of the class hierarchy.

Each type is one of:

• A built-in type
  • Part of the Common Type System (CTS)
  • Available in C# using a keyword for the type, e.g. int, float, string, array, object
• A custom type
  • Defined in the .NET Framework class library
• A user-defined type
  • You define in your code

Here is the class hierarchy for all types.  Indentation indicates that a class derives from class listed above it.  Parentheses indicate C# keywords for built-in types.

• System.Object  (object)
  • System.ValueType
    • System.Enum
      • user-defined enum types
    • System.Boolean  (bool)
    • System.Byte  (byte)
    • System.SByte  (sbyte)
    • System.Int16  (short)
    • System.UInt16  (ushort)
    • System.Int32  (int)
    • System.UInt32  (uint)
    • System.Int64  (long)
    • System.UInt64  (ulong)
    • System.Single  (float)
    • System.Double  (double)
    • System.Decimal  (decimal)
    • System.Char  (char)
    • System.Void  (void)
    • System.DateTime
    • System.Guid
    • System.TimeSpan
    • System.IntPtr
    • System.UIntPtr
    • user-defined struct types
  • System.String  (string)
  • System.Array  (array)
  • System.Type
  • System.Delegate
    • System.MulticastDelegate  (delegate)
  • custom types in .NET Framework
  • user-defined types
  • boxed value types