Common Type System—Namespaces Organizing Types

Visual C# Tutorials

.NET Framework Tutorials

Common Type System Type Systems Intro § Types and Objects § Type Unification § Reference, Value Types § Accessibility, Visibility § Type Members § Fields § Methods § Locals Overloading Argument Passing Style Pass-by-Value and Pass-by-Reference Output Parameters Managed Pointers Variable Argument Methods Methods, Subclassing Virtuals, Overriding New Slots Exception Handlers Constructors, Instantiation § Default Constructors Value Construction Constructor Chaining Field Initialization Type Initializers Unhandled Exceptions Properties § Indexers Mixed Mode Accessibility Events Operator Overloading Coercion Subclassing, Polymorphism Styles of Inheritance § Implementation Inheritance Interface Inheritance Abstract Classes Interfaces § Method Dispatch Multiple Inheritance Private Interface Inheritance Private Inheritance Accessibility Interface Reimplementation Abstract and Interface? Sealing Types and Methods Runtime Type Checking Namespaces: Organizing Types § Define a Namespace Namespace Resolution Special Types § Delegates § CTS Support Co- and Contravariance Anonymous Delegates Custom Attributes Enumerations § Flags-Style Limitations Helper Methods Generics § Further Reading §

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Namespaces: Organizing Types

All useful programming environments have a module and packaging system. Aside from assemblies and modules, which provide physical packaging for distribution and reuse namespaces provide a logical packaging facility. As part of a type’s naming, it can also be assigned a namespace. The type’s namespace plus its name is called its fully qualified name. All types included in the .NET Framework have namespaces, most of them starting with System, although some product-specific ones start with Microsoft. The CTS has no concept of namespaces. All types and references to them are emitted using their fully qualified name.

Namespaces are hierarchical in nature. We refer to them by their order, so, for example, the root is the first level, the set below that are second level, and so on. For example, consider that the fully qualified name System.Collections.Generic.List<T>. System is the first level, Collections is the second level, Generic is the third level, and List<T> is the type name. Namespaces really have nothing to do technology-wise with the assemblies in which they live. Types in the same namespace can span multiple assemblies. Most developers tend to have a near 1:1 relationship between namespaces and assemblies, however, to make locating types easier. For example, rather than a user having to consider a set of assemblies when looking for a certain type in a certain namespace, having a 1:1 correspondence limits the choice to one.