I'm getting the error: "Type doesn't conform to protocol 'Comparable'" when trying to compile a Swift code from manual

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I tried the example below from the Swift - Protocols manual page, but I am getting the compiler error:

error: type 'SkillLevel' does not conform to protocol 'Comparable':

enum SkillLevel: Comparable {
    case beginner
    case intermediate
    case expert(stars: Int)
}
var levels = [SkillLevel.intermediate, SkillLevel.beginner,
              SkillLevel.expert(stars: 5), SkillLevel.expert(stars: 3)]
for level in levels.sorted() {
    print(level)
}

Xcode suggests to add the function below to make it to conform to Comparable:

static func < (lhs: SkillLevel, rhs: SkillLevel) -> Bool {
    <#code#>
}

From the manual:

Swift provides a synthesized implementation of Comparable for enumerations that don’t have a raw value. If the enumeration has associated types, they must all conform to the Comparable protocol. To receive a synthesized implementation of <, declare conformance to Comparable in the file that contains the original enumeration declaration, without implementing a < operator yourself. The Comparable protocol’s default implementation of <=, >, and >= provides the remaining comparison operators.

I'm not sure if the enumeration in the code above has a raw value, but if it doesn't, shouldn't the code had compiled without the implementation of the function "<"?

swift
1 Answers

Automatically generating the < operator works if you have something similar to a plain C enum; just the cases and nothing else. But here one of the cases has an associated type, so the compiler doesn't want to guess how you want values ordered.

user_32554550
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