:: operator - the namespace alias operator
Use the namespace alias qualifier ::
to access a member of an aliased namespace. You can use the ::
qualifier only between two identifiers. The left-hand identifier can be one of a namespace alias, an extern alias, or the global
alias. For example:
A namespace alias created with a using alias directive:
using forwinforms = System.Drawing; using forwpf = System.Windows; public class Converters { public static forwpf::Point Convert(forwinforms::Point point) => new forwpf::Point(point.X, point.Y); }
An extern alias.
The
global
alias, which is the global namespace alias. The global namespace is the namespace that contains namespaces and types that aren't declared inside a named namespace. When used with the::
qualifier, theglobal
alias always references the global namespace, even if there's the user-definedglobal
namespace alias.The following example uses the
global
alias to access the .NET System namespace, which is a member of the global namespace. Without theglobal
alias, the user-definedSystem
namespace, which is a member of theMyCompany.MyProduct
namespace, would be accessed:namespace MyCompany.MyProduct.System { class Program { static void Main() => global::System.Console.WriteLine("Using global alias"); } class Console { string Suggestion => "Consider renaming this class"; } }
Note
The
global
keyword is the global namespace alias only when it's the left-hand identifier of the::
qualifier.
You can also use the .
token to access a member of an aliased namespace. However, the .
token is also used to access a type member. The ::
qualifier ensures that its left-hand identifier always references a namespace alias, even if there exists a type or namespace with the same name.
C# language specification
For more information, see the Namespace alias qualifiers section of the C# language specification.
See also
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