Enumerations

Enumerations are sets of symbolic names bound to unique, constant values, which can be compared by identity.

Enum declaration

Enums are declared using the enum keyword, followed by the name of the enum, the raw type after a colon, and the requirements, which must be enclosed in opening and closing braces.

The raw type must be an integer subtype (e.g., UInt8 or Int128).

Enum cases are declared using the case keyword, followed by the name of the enum case.

Enum cases must be unique. Each enum case has a raw value, which is the index of the case among all cases.

The raw value of an enum case can be accessed through the rawValue field.

The enum cases can be accessed by using the name as a field on the enum or by using the enum constructor, which requires providing the raw value as an argument. The enum constructor returns the enum case with the given raw value, if any, or nil if no such case exists.

Enum cases can be compared using the equality operators == and !=.

Working with an enum declaration

1. Declare an enum named Color, which has the raw value type UInt8, and declare three enum cases (red, green, and blue):

   
   

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   access(all)

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   enum Color: UInt8 {

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   access(all)

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   case red

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   access(all)

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   case green

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   access(all)

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   case blue

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   }

   
   

2. Declare a variable that has the enum type Color and initialize it to the enum case blue of the enum:

   
   

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   let blue: Color = Color.blue

   
   

3. Get the raw value of the enum case blue. Since it is the third case, it has an index of 2:

   
   

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   blue.rawValue // is `2`

   
   

4. Get the green enum case of the enum Color by using the enum constructor and providing the raw value of the enum case green, 1. Since the enum case green is the second case, it has an index of 1:

   
   

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   let green: Color? = Color(rawValue: 1) // is `Color.green`

   
   

5. Get the enum case of the enum Color with the raw value 5. As there are only three cases, the maximum raw value/index is 2:

   
   

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   let nothing = Color(rawValue: 5) // is `nil`

   
   

   Enum cases can be compared:

   
   

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   Color.red == Color.red // is `true`

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   Color(rawValue: 1) == Color.green // is `true`

   
   

   Different enum cases are not the same:

   
   

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   Color.red != Color.blue // is `true`