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CA2217: Do not mark enums with FlagsAttribute

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Property Value
Rule ID CA2217
Title Do not mark enums with FlagsAttribute
Category Usage
Fix is breaking or non-breaking Non-breaking
Enabled by default in .NET 9 No

Cause

An enumeration is marked with FlagsAttribute and it has one or more values that are not powers of two or a combination of the other defined values on the enumeration.

By default, this rule only looks at externally visible enumerations, but this is configurable.

Rule description

An enumeration should have FlagsAttribute present only if each value defined in the enumeration is a power of two or a combination of defined values.

How to fix violations

To fix a violation of this rule, remove FlagsAttribute from the enumeration.

When to suppress warnings

Do not suppress a warning from this rule.

Configure code to analyze

Use the following option to configure which parts of your codebase to run this rule on.

You can configure this option for just this rule, for all rules it applies to, or for all rules in this category (Usage) that it applies to. For more information, see Code quality rule configuration options.

Include specific API surfaces

You can configure which parts of your codebase to run this rule on, based on their accessibility. For example, to specify that the rule should run only against the non-public API surface, add the following key-value pair to an .editorconfig file in your project:

dotnet_code_quality.CAXXXX.api_surface = private, internal

Examples

The following code shows an enumeration, Color, that contains the value 3. 3 is not a power of two, or a combination of any of the defined values. The Color enumeration shouldn't be marked with FlagsAttribute.

// Violates this rule    
[FlagsAttribute]
public enum Color
{
    None = 0,
    Red = 1,
    Orange = 3,
    Yellow = 4
}

Imports System

Namespace Samples

    ' Violates this rule    
    <FlagsAttribute()> _
    Public Enum Color

        None = 0
        Red = 1
        Orange = 3
        Yellow = 4

    End Enum
End Namespace

The following code shows an enumeration, Days, that meets the requirements for being marked with FlagsAttribute:

[FlagsAttribute]
public enum Days
{
    None = 0,
    Monday = 1,
    Tuesday = 2,
    Wednesday = 4,
    Thursday = 8,
    Friday = 16,
    All = Monday | Tuesday | Wednesday | Thursday | Friday
}

Imports System
Namespace Samples

    <FlagsAttribute()> _
    Public Enum Days

        None = 0
        Monday = 1
        Tuesday = 2
        Wednesday = 4
        Thursday = 8
        Friday = 16
        All = Monday Or Tuesday Or Wednesday Or Thursday Or Friday

    End Enum
End Namespace

CA1027: Mark enums with FlagsAttribute

See also