fileprivate enum cases in pseudo-Swift https://twitter.com/inamiy/status/1322750532197380096

fileprivate-enum-cases.swift

/// Pseudo-Swift: public / fileprivate enum cases
public enum Action {
    public case foo
    public case bar(Int)
    
    // fileprivate enum cases, where pattern matches are only allowed in this file.
    // From outside, only using switch statement's `default` is possible.
    // (NOTE: `private` won't make sense)
    //
    // This is useful to define private-Action values.
    fileprivate case baz1
    fileprivate case baz2(Bool)
}

// is essentially equal (isomorphic) to the following workaround Swift code:

public enum Action {
    case foo
    case bar(Int)
    case baz1(Signature)
    case baz2(Bool, Signature)

    /// Public type, but only initializable in this file
    /// so that `.baz1` and `.baz2` are never initializable (never exists) from outside.
    public struct Signature {
        fileprivate init() {}
    }
}