CA1008: Enums should have zero value
Property | Value |
---|---|
Rule ID | CA1008 |
Title | Enums should have zero value |
Category | Design |
Fix is breaking or non-breaking | Non-breaking - When you're prompted to add a None value to a non-flag enumeration. Breaking - When you're prompted to rename or remove any enumeration values. |
Enabled by default in .NET 9 | No |
An enumeration without an applied System.FlagsAttribute does not define a member that has a value of zero. Or, an enumeration that has an applied FlagsAttribute defines a member that has a value of zero but its name is not 'None'. Or, the enumeration defines multiple, zero-valued members.
By default, this rule only looks at externally visible enumerations, but this is configurable.
The default value of an uninitialized enumeration, just like other value types, is zero. A non-flags-attributed enumeration should define a member that has the value of zero so that the default value is a valid value of the enumeration. If appropriate, name the member 'None' (or one of the additional permitted names). Otherwise, assign zero to the most frequently used member. By default, if the value of the first enumeration member is not set in the declaration, its value is zero.
If an enumeration that has the FlagsAttribute applied defines a zero-valued member, its name should be 'None' (or one of the additional permitted names) to indicate that no values have been set in the enumeration. Using a zero-valued member for any other purpose is contrary to the use of the FlagsAttribute in that the AND
and OR
bitwise operators are useless with the member. This implies that only one member should be assigned the value zero. If multiple members that have the value zero occur in a flags-attributed enumeration, Enum.ToString()
returns incorrect results for members that are not zero.
To fix a violation of this rule for non-flags-attributed enumerations, define a member that has the value of zero; this is a non-breaking change. For flags-attributed enumerations that define a zero-valued member, name this member 'None' and delete any other members that have a value of zero; this is a breaking change.
Do not suppress a warning from this rule except for flags-attributed enumerations that have previously shipped.
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 CA1008
// The code that's violating the rule is on this line.
#pragma warning restore CA1008
To disable the rule for a file, folder, or project, set its severity to none
in the configuration file.
[*.{cs,vb}]
dotnet_diagnostic.CA1008.severity = none
For more information, see How to suppress code analysis warnings.
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 (Design) that it applies to. For more information, see Code quality rule configuration options.
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
In .NET 7 and later versions, you can configure other allowable names for a zero-value enumeration field, besides None
. Separate multiple names by the |
character. The following table shows some examples.
Option value | Summary |
---|---|
dotnet_code_quality.CA1008.additional_enum_none_names = Never |
Allows both None and Never |
dotnet_code_quality.CA1008.additional_enum_none_names = Never|Nothing |
Allows None , Never , and Nothing |
The following example shows two enumerations that satisfy the rule and an enumeration, BadTraceOptions
, that violates the rule.
using System;
namespace ca1008
{
public enum TraceLevel
{
Off = 0,
Error = 1,
Warning = 2,
Info = 3,
Verbose = 4
}
[Flags]
public enum TraceOptions
{
None = 0,
CallStack = 0x01,
LogicalStack = 0x02,
DateTime = 0x04,
Timestamp = 0x08,
}
[Flags]
public enum BadTraceOptions
{
CallStack = 0,
LogicalStack = 0x01,
DateTime = 0x02,
Timestamp = 0x04,
}
class UseBadTraceOptions
{
static void MainTrace()
{
// Set the flags.
BadTraceOptions badOptions =
BadTraceOptions.LogicalStack | BadTraceOptions.Timestamp;
// Check whether CallStack is set.
if ((badOptions & BadTraceOptions.CallStack) ==
BadTraceOptions.CallStack)
{
// This 'if' statement is always true.
}
}
}
}
Imports System
Namespace ca1008
Public Enum TraceLevel
Off = 0
AnError = 1
Warning = 2
Info = 3
Verbose = 4
End Enum
<Flags>
Public Enum TraceOptions
None = 0
CallStack = &H1
LogicalStack = &H2
DateTime = &H4
Timestamp = &H8
End Enum
<Flags>
Public Enum BadTraceOptions
CallStack = 0
LogicalStack = &H1
DateTime = &H2
Timestamp = &H4
End Enum
Class UseBadTraceOptions
Shared Sub Main1008()
' Set the flags.
Dim badOptions As BadTraceOptions =
BadTraceOptions.LogicalStack Or BadTraceOptions.Timestamp
' Check whether CallStack is set.
If ((badOptions And BadTraceOptions.CallStack) =
BadTraceOptions.CallStack) Then
' This 'If' statement is always true.
End If
End Sub
End Class
End Namespace
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