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Generic Enums

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Generic Enums

In the design of generic enum types in the Cangjie programming language, the Option type serves as a classic example. For a detailed description of Option, please refer to the Option Type chapter. The Option type is used to represent a value that may be empty for a certain type. Thus, Option can indicate computational failure for a particular type. Since the specific type of failure is indeterminate, it's evident that Option is a generic type requiring the declaration of type parameters.

As shown, Option has two variants: Some(T), which represents a successful return value, and None, which indicates an empty result. The getOrThrow function extracts the inner value from Some(T), returning a result of type T. If the parameter is None, it directly throws an exception.

For example, to define a safe division operation (since division computations may fail), we can return None when the divisor is 0, otherwise returning a result wrapped in Some:

This approach ensures the program won't throw arithmetic exceptions during runtime when encountering division by zero.

cangjie

package std.core // `Option` is defined in std.core.

public enum Option<T> {
      Some(T)
    | None

    public func getOrThrow(): T {
        match (this) {
            case Some(v) => v
            case None => throw NoneValueException()
        }
    }
    // ...
}

cangjie

func safeDiv(a: Int64, b: Int64): Option<Int64> {
    var res: Option<Int64> = match (b) {
                case 0 => None
                case _ => Some(a/b)
            }
    return res
}