CA1069: Enums should not have duplicate values

Property	Value
Rule ID	CA1069
Title	Enums should not have duplicate values
Category	Design
Fix is breaking or non-breaking	Breaking
Enabled by default in .NET 8	As suggestion

Cause

An enumeration has multiple members which are explicitly assigned the same constant value.

Rule description

Every enum member should either have a unique constant value or be explicitly assigned with a prior member in the enum to indicate explicit intent of sharing value. For example:

enum E
{
   Field1 = 1,
   AnotherNameForField1 = Field1,   // This is fine
   Field2 = 2,
   Field3 = 2,   // CA1069: This is not fine. Either assign a different constant value or 'Field2' to indicate explicit intent of sharing value.
}

This rule helps in catching functional bugs introduced from the following scenarios:

• Accidental typing mistakes, where the user accidentally typed the same constant value for multiple members.
• Copy paste mistakes, where the user copied an existing member definition, then renamed the member but forgot to change the value.
• Merge resolution from multiple branches, where a new member was added with a different name but the same value in different branches.

How to fix violations

To fix a violation, either assign a new unique constant value or assign with a prior member in the enum to indicate explicit intent of sharing the same value. For example, the following code snippet shows a violation of the rule and couple of ways to fix the violation:

enum E
{
   Field1 = 1,
   AnotherNameForField1 = Field1,   // This is fine
   Field2 = 2,
   Field3 = 2,   // CA1069: This is not fine. Either assign a different constant value or 'Field2' to indicate explicit intent of sharing value.
}

enum E
{
   Field1 = 1,
   AnotherNameForField1 = Field1,   // This is fine
   Field2 = 2,
   Field3 = 3,   // This is now fine
}

enum E
{
   Field1 = 1,
   AnotherNameForField1 = Field1,   // This is fine
   Field2 = 2,
   Field3 = Field2,   // This is also fine
}

When to suppress warnings

Do not suppress violations of this rule.

See also

• Design rules