CA1008: Enums should have zero value
Non-breaking - When you are prompted to add a None value to a non-flag enumeration.Breaking - When you are prompted to rename or remove any enumeration values.
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'. Otherwise, assign zero to the most frequently used member. Note that, 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' 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. Note that 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.
The following example shows two enumerations that satisfy the rule and an enumeration, BadTraceOptions, that violates the rule.
Imports System Namespace DesignLibrary Public Enum TraceLevel Off = 0 AnError = 1 Warning = 2 Info = 3 Verbose = 4 End Enum <Flags> _ Public Enum TraceOptions None = 0 CallStack = &H01 LogicalStack = &H02 DateTime = &H04 Timestamp = &H08 End Enum <Flags> _ Public Enum BadTraceOptions CallStack = 0 LogicalStack = &H01 DateTime = &H02 Timestamp = &H04 End Enum Class UseBadTraceOptions Shared Sub Main() ' Set the flags. Dim badOptions As BadTraceOptions = _ BadTraceOptions.LogicalStack Or BadTraceOptions.Timestamp ' Check whether CallStack is set. If((badOptions And BadTraceOptions.CallStack) = _ BadTraceOptions.CallStack) ' This 'If' statement is always true. End If End Sub End Class End Namespace