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CA1700: Do not name enum values 'Reserved'

TypeName

DoNotNameEnumValuesReserved

CheckId

CA1700

Category

Microsoft.Naming

Breaking Change

Breaking

The name of an enumeration member contains the word "reserved".

This rule assumes that an enumeration member that has a name that contains "reserved" is not currently used but is a placeholder to be renamed or removed in a future version. Renaming or removing a member is a breaking change. You should not expect users to ignore a member just because its name contains "reserved", nor can you rely on users to read or abide by documentation. Furthermore, because reserved members appear in object browsers and smart integrated development environments, they can cause confusion about which members are actually being used.

Instead of using a reserved member, add a new member to the enumeration in the future version. In most cases the addition of the new member is not a breaking change, as long as the addition does not cause the values of the original members to change.

In a limited number of cases the addition of a member is a breaking change even when the original members retain their original values. Primarily, the new member cannot be returned from existing code paths without breaking callers that use a switch (Select in Visual Basic) statement on the return value that encompasses the whole member list and that throw an exception in the default case. A secondary concern is that client code might not handle the change in behavior from reflection methods such as Enum.IsDefined. Accordingly, if the new member has to be returned from existing methods or a known application incompatibility occurs because of poor reflection usage, the only nonbreaking solution is to:

  1. Add a new enumeration that contains the original and new members.

  2. Mark the original enumeration with the System.ObsoleteAttribute attribute.

Follow the same procedure for any externally visible types or members that expose the original enumeration.

To fix a violation of this rule, remove or rename the member.

It is safe to suppress a warning from this rule for a member that is currently used or for libraries that have previously shipped.

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