Question:

In Swift enumerations, what’s the difference between raw values and associated values?

Answer:

Raw values are used to associate constant (literal) values to enum cases. The value type is part of the enum type, and each enum case must specify a unique raw value (duplicate values are not allowed).

The following example shows an enum with raw values of type Int:

enum IntEnum : Int {
    case ONE = 1
    case TWO = 2
    case THREE = 3
}

An enum value can be converted to its raw value by using the rawValue property:

var enumVar: IntEnum = IntEnum.TWO
var rawValue: Int = enumVar.rawValue

A raw value can be converted to an enum instance by using a dedicated initializer:

var enumVar: IntEnum? = IntEnum(rawValue: 1)

Associated values are used to associate arbitrary data to a specific enum case. Each enum case can have zero or more associated values, declared as a tuple in the case definition:

enum AssociatedEnum {
    case EMPTY
    case WITH_INT(value: Int)
    case WITH_TUPLE(value: Int, text: String, data: [Float])
}

Whereas the type(s) associated to a case are part of the enum declaration, the associated value(s) are instance specific, meaning that an enum case can have different associated values for different enum instances.


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