CA1050: Declare types in namespaces

Article
04/22/2023

Property	Value
Rule ID	CA1050
Title	Declare types in namespaces
Category	Design
Fix is breaking or non-breaking	Breaking
Enabled by default in .NET 8	As suggestion

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 Test();
        Console.WriteLine(t1.ToString());

        ca1050.Test t2 = new ca1050.Test();
        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

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