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CA1050: Declare types in namespaces

TypeName

DeclareTypesInNamespaces

CheckId

CA1050

Category

Microsoft.Design

Breaking Change

Breaking

A public or protected type is defined outside the scope of a named namespace.

Types are declared in namespaces to prevent name collisions, and as a way to organize related types in an object hierarchy. Types that are outside any named namespace are in a global namespace that cannot be referenced in code.

To fix a violation of this rule, place the type in a namespace.

Although you never have to suppress a warning from this rule, it is safe to do this when the assembly will never be used together with other assemblies.

The following example shows a library that has a type incorrectly declared outside a namespace, and a type that has the same name declared in a namespace.

Imports System 

' Violates rule: DeclareTypesInNamespaces. 
Public Class Test     

    Public Overrides Function ToString() As String         
        Return "Test does not live in a namespace!"     
    End Function  

End Class  

Namespace GoodSpace  

    Public Class Test 

        Public Overrides Function ToString() As String             
            Return "Test lives in a namespace!"         
        End Function   

    End Class  

End Namespace

The following application uses the library that was defined previously. Note that the type that is declared outside a namespace is created when the name Test is not qualified by a namespace. Note also that to access the Test type in Goodspace, the namespace name is required.

Imports System

Namespace ApplicationTester

    Public Class MainHolder

        Public Shared Sub Main()
            Dim t1 As New Test()
            Console.WriteLine(t1.ToString())

            Dim t2 As New GoodSpace.Test()
            Console.WriteLine(t2.ToString())
        End Sub 

    End Class 

End Namespace
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