Understanding the Common Type Specification (CTS)

A Type refers to a collection of classes, interfaces, delegates, and structures supported by the Common Language Runtime. Microsoft .NET also allows you to create your own user-defined types. Moreover, you can group the user-defined types into unique namespaces. As previously stated, all objects derive from System.Object. Table 5-4 provides information about the .NET namespaces.

Table 5-4: .NET Namespaces

.NET Namespace	Meaning
System	Contains a collection of classes referencing primitive types, math manipulations, garbage collection, debugging, etc.
System.Collections	Defines container objects, for example, ArrayLists, Queues, etc.
System.Data.Oledb System.Data System.Data.Common System.Data.SqlClient	Pertains to all database functionality.
System.IO	Comprises file I/O.
System.Reflection System.Reflection.Emit	Supports IL code and assembly examination at runtime. System.Reflection.Emit allows you to create dynamic assemblies on the fly.
System.Net	Hosts Types relating to network application design.
System.Diagnostics	Facilitates language-agnostic diagnosis.
System.Drawing.System.Drawing2D System.Drawing.Printing	Supports all GDI, bitmaps, icons, and fonts.
System.Runtime.InteropServices System.Runtime.Remoting	Offers interoperability between managed and unmanaged code, for example, COM Servers, Win32 DLLs, etc.
System.Threading	Facilitates multithreading. This includes Types Mutex, Timeout, and Thread.
System.Security	Supports .NET security, for example, CodeAccessPermissions.
System.Windows.Forms	Enables dialog box construction, windows, MessageBox.Show, etc.
System.Web	Provides support for all web services, web application development, and ASP.NET (the presentation layer).
System.XML	Contains a set of classes representing core XML primitives and types, thereby facilitating interaction with XML data.

In Visual Basic .NET, the CTS Structure replaces VB Types. Whereas VB 6.0 supported the Type keyword, thereby enabling developers to create user-defined types, the .NET keyword Structure defines numerical types, for example, complex numbers. As observed in our System.Reflection.Emit runtime application, DynamicAssembly, the Common Type Specification provides information on all data types supported by the runtime. Simply put, the CTS describes precisely how the disparate data types interact with each other courtesy of the assembly manifest, both at design time and runtime. This demonstrates how .NET reusable binaries can intermingle across all platforms targeting the Framework. Structures implement a great number of interfaces.

Note

The list of tree icons for viewing an assembly, provided in the earlier section “Reading Metadata,” displayed a magenta rectangle marked “S.” This icon denotes a static method, meaning the method is sealed. Therefore, structures may not derive from other base types.

Before turning our discussion to .NET modules, let’s finish this examination of CTS Types. Table 5-5 displays the CTS intrinsic Types. You can see how all languages share the same data type declared and defined in Microsoft .NET class libraries.

Table 5-5: Microsoft .NET Intrinsic Types and Their Representations in Other Languages

Microsoft .NET Types	Visual Basic .NET Type Representation	C# Type Representation	C++ with Managed Extensions Representation
System.Byte	Byte	byte	char
System.SByte	Not supported	sbyte	signed char
System.Int16	Short	short	short
System.Int32	Integer	int	int or long
System.Int64	Long	long	_64
System.UInt16	Not supported	ushort	unsigned short
System.UInt32	Not supported	uint	unsigned int or unsigned long
System.UInt64	Not supported	ulong	unsigned_int64
System.Single	Single	float	float
System.Double	Double	double	double
System.Object	Object	object	Object
System.Char	Char	char	_wchar_t
System.String	String	string	String
System.Decimal	Decimal	decimal	Decimal
System.Boolean	Boolean	bool	bool

.NET Modules

A .NET module is a representation of a class type. Public functions, subroutines, and variables defined within module scope are shared members. They are visible to an entire application.

Note

You may not create modules. For an example, refer to our IFCE Assembly module:

ModuleBuilder module = assembly.DefineDynamicModule
("MyIFCEAssembly", "MyIFCEAssembly.dll");