CA1050: Declare types in namespaces

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.

Suppress a warning

If you just want to suppress a single violation, add preprocessor directives to your source file to disable and then re-enable the rule.

#pragma warning disable CA1050
// The code that's violating the rule is on this line.
#pragma warning restore CA1050

To disable the rule for a file, folder, or project, set its severity to none in the configuration file.

[*.{cs,vb}]
dotnet_diagnostic.CA1050.severity = none

For more information, see How to suppress code analysis warnings.

Example 1

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.

// Violates rule: DeclareTypesInNamespaces.
using System;

public class Test
{
 public override string ToString()
 {
 return "Test does not live in a namespace!";
 }
}

namespace ca1050
{
 public class Test
 {
 public override string ToString()
 {
 return "Test lives in a namespace!";
 }
 }
}

' 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 ca1050

 Public Class Test

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

 End Class

End Namespace

Example 2

The following application uses the library that was defined previously. The type that's declared outside a namespace is created when the name Test is not qualified by a namespace. To access the Test type that's declared inside a namespace, the namespace name is required.

public class MainHolder
{
 public static void Main1050()
 {
 Test t1 = new();
 Console.WriteLine(t1.ToString());

 ca1050.Test t2 = new();
 Console.WriteLine(t2.ToString());
 }
}

Public Class MainHolder

 Public Shared Sub Main1050()
 Dim t1 As New Test()
 Console.WriteLine(t1.ToString())

 Dim t2 As New ca1050.Test()
 Console.WriteLine(t2.ToString())
 End Sub

End Class