Understanding the .NET Framework - The Common Type System

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The CTS implements the formal specifications for the type system used by the .NET Framework. All data types represented by the CTS are objects. The CTS defines how a type is defined and the operators that it can accept. One of the primary goals of the CTS is to enable deep language integration by allowing code that's written in one language to be inherited and used by another language. Sharing a common system of data types is one of the most fundamental building blocks that enable this to happen.

Classes of Types

The .NET Framework supports two basic classes of types: value types and reference types. The following section describes these types in more detail.

Value Types - Value types are very similar to the built-in data types provided by most programming languages. Typical data types that are used to store variable values include characters, integers, strings, and floating-point numbers. In the .NET Framework, they are termed value types because they are copied when they are passed as arguments. In other words, they are passed by value. The .NET Framework stores value types on the stack. Table 2-4 lists the value type supported by the .NET Framework along with their VB.NET and C# data type keywords. 

Type	Description	VB.NET	C#
Boolean	A Boolean value (true or false)	Boolean	bool
Byte	An 8-bit unsigned integer	Byte	byte
Char	A Unicode (16-bit) character	Char	char
Decimal	A 96-bit decimal value	Decimal	decimal
Double	A double-precision (64-bit) floating-point number	Double	double
Int16	A 16-bit signed integer	Short	short
Int32	A 32-bit signed integer	Integer	int
Int64	A 64-bit signed integer	Long	long
IntPtr	A signed integer whose size depends on the underlying platform	IntPtr	IntPtr
Object	The root of the object hierarchy	Object	object
SByte	An 8-bit signed integer	SByte	sbyte
Single	A single-precision (32-bit) floating-point number	Single	float
String	An immutable, fixed-length string of Unicode characters	String	string
UInt16	A 16-bit unsigned integer	UInt16	ushort
UInt32	A 32-bit unsigned integer	UInt32	uint
UInt64	A 64-bit unsigned integer	UInt64	ulong
UIntPtr	An unsigned integer whose size depends on the underlying platform	UIntPtr	UIntPtr

Table 2-4. CTS Value Types

Reference Types - Reference types store a reference to the value's memory address, and are allocated on the heap. Reference types can be self-describing types, pointer types, or interface types. Unlike value types, reference types are passed between procedures using the address. In other words, a reference to the original object is passed rather than a copy of that object, as is the case with value types.

Type	Description	VB.NET	C#
Classes	A class is a data structure that may contain data members (constants, variables, and events), function members (methods, properties, indexers, operators, and constructors), and nested types.	Class	class
Delegates	A delegate is a reference type that refers to a shared method of a type or to an instance method of an object.	Delegate	delegate
Arrays	An array is a data structure that contains a number of variables (elements of the array).	Dim MyArray(5) As Integer	int[] myArray=
Interfaces	Interfaces are implemented by other types to guarantee that they support certain operations. An interface defines a contract. A class or structure that implements an interface must adhere to that contract.	Interface	interface
Pointers	Pointers reference blocks of memory. There are three kinds of pointers supported by the runtime: managed pointers, unmanaged pointers, and unmanaged function pointers.	N/A	int*

Table 2-5. CTS Reference Types

This is chapter two of ADO.NET: The Complete Reference, by Michael and Denielle Otey (McGraw-Hill/Osborne, ISBN 0-07-222898-9, 2003). Check it out at your favorite bookstore today. Buy this book now.

Next: The .NET Framework Class Library >>
 

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