CA1050: Declare types in namespaces

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TypeName DeclareTypesInNamespaces
CheckId CA1050
Category Microsoft.Design
Breaking Change Breaking

Cause

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

Rule Description

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.

How to Fix Violations

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

When to Suppress Warnings

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.

Example

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.

using System;

// Violates rule: DeclareTypesInNamespaces.
public class Test
{
   public override string ToString()
   {
      return "Test does not live in a namespace!";
   }
}

namespace GoodSpace
{
   public class Test
   {
      public override string ToString()
      {
         return "Test lives 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

Example

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.

using System;

namespace ApplicationTester
{
    public class MainHolder
    {
        public static void Main()
        {
            Test t1 = new Test();
            Console.WriteLine(t1.ToString());

            GoodSpace.Test t2 = new GoodSpace.Test();
            Console.WriteLine(t2.ToString());
        }
    }
}
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