Duplicate Enum Cases

ID

swift.duplicate_enum_cases

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Swift

Tags

enum, reliability

Description

Reports two or more enum cases in the same declaration that share the same raw value. Swift’s compiler emits only a warning, but EnumType(rawValue: x) silently returns one of the conflicting cases — almost always a bug.

enum Status: Int {
    case active = 1                       // FLAW
    case inactive = 1                     // FLAW
    case pending = 2                      // OK
}

enum Color: String {
    case red = "red"                      // FLAW
    case crimson = "red"                  // FLAW
    case blue = "blue"                    // OK
}

Rationale

The compiler warning is easy to miss in a large project, and the runtime behaviour of init(rawValue:) is unspecified for conflicting raw values. Two cases that should be distinct become indistinguishable at serialization boundaries (JSON decoding, persistence, IPC).

Remediation

Pick distinct raw values, or rethink the model:

enum Status: Int {
    case active = 1
    case inactive = 2
    case pending = 3
}

// If two names really should map to the same value, use a static constant
// rather than a duplicate case.
enum Color: String {
    case red = "red"
    case blue = "blue"
    static let crimson = Color.red
}

References