namespace
The namespace keyword is used to declare a scope that contains a set of related objects. You can use a namespace to organize code elements and to create globally unique types.
namespace SampleNamespace
{
class SampleClass { }
interface ISampleInterface { }
struct SampleStruct { }
enum SampleEnum { a, b }
delegate void SampleDelegate(int i);
namespace Nested
{
class SampleClass2 { }
}
}
File scoped namespace declarations enable you to declare that all types in a file are in a single namespace. File scoped namespace declarations are available with C# 10. The following example is similar to the previous example, but uses a file scoped namespace declaration:
using System;
namespace SampleFileScopedNamespace;
class SampleClass { }
interface ISampleInterface { }
struct SampleStruct { }
enum SampleEnum { a, b }
delegate void SampleDelegate(int i);
The preceding example doesn't include a nested namespace. File scoped namespaces can't include additional namespace declarations. You cannot declare a nested namespace or a second file-scoped namespace:
namespace SampleNamespace;
class AnotherSampleClass
{
public void AnotherSampleMethod()
{
System.Console.WriteLine(
"SampleMethod inside SampleNamespace");
}
}
namespace AnotherNamespace; // Not allowed!
namespace ANestedNamespace // Not allowed!
{
// declarations...
}
Within a namespace, you can declare zero or more of the following types:
- class
- interface
- struct
- enum
- delegate
- nested namespaces can be declared except in file scoped namespace declarations
The compiler adds a default namespace. This unnamed namespace, sometimes referred to as the global namespace, is present in every file. It contains declarations not included in a declared namespace. Any identifier in the global namespace is available for use in a named namespace.
Namespaces implicitly have public access. For a discussion of the access modifiers you can assign to elements in a namespace, see Access Modifiers.
It's possible to define a namespace in two or more declarations. For example, the following example defines two classes as part of the MyCompany namespace:
namespace MyCompany.Proj1
{
class MyClass
{
}
}
namespace MyCompany.Proj1
{
class MyClass1
{
}
}
The following example shows how to call a static method in a nested namespace.
namespace SomeNameSpace
{
public class MyClass
{
static void Main()
{
Nested.NestedNameSpaceClass.SayHello();
}
}
// a nested namespace
namespace Nested
{
public class NestedNameSpaceClass
{
public static void SayHello()
{
Console.WriteLine("Hello");
}
}
}
}
// Output: Hello
C# language specification
For more information, see the Namespaces section of the C# language specification. For more information on file scoped namespace declarations, see the feature specification.
