SwiftRexMacros

Macros to help automating SwiftRex boilerplate

Prism

A macro that produces predicates and prisms for all cases of an Enum. Predicates will be Bool properties in the format isCaseA that returns true whenever that instance points to the caseA case of the enum. Prism is a property with the same name as the case, but for the instance of the enum. If the instance points to that case, the variable will return a tuple of all associated values of that case, or instance of Void () for case without associated values. However, if the instance points to another case, it will return nil. This is extremely useful for using KeyPaths.

Example of predicates:

@Prism
enum Color {
    case red, green, blue
}

produces:

extension Color {
    var isRed: Bool {
        if case .red = self { true } else { false }
    }
    var isGreen: Bool {
        if case .green = self { true } else { false }
    }
    var isBlue: Bool {
        if case .blue = self { true } else { false }
    }
}

usage:

let color1 = Color.red
color1.isRed // true
color1.isGreen // false
color1.isBlue // false

Example os prism:

@Prism
enum Contact {
    case email(address: String)
    case phone(countryCode: String, number: String)
    case letter(street: String, house: String, postalCode: String, city: String, state: String, country: String)
    case noContact
}

produces:

extension Contact {
    var email: String? {
        guard case let .email(address) = self else { return nil }
        return address
    }
    var phone: (countryCode: String, number: String)? {
        guard case let .phone(countryCode, number) = self else { return nil }
        return (countryCode: countryCode, number: number)
    }
    var letter: (street: String, house: String, postalCode: String, city: String, state: String, country: String)? {
        guard case let .letter(street, house, postalCode, city, state, country) = self else { return nil }
        return (street: street, house: house, postalCode: postalCode, city: city, state: state, country: country)
    }
    var noContact: Void? {
        guard case .noContact = self else { return nil }
        return ()
    }
}

Please notice that the Void case is important not only for consistency, but for more advanced cases of composition. Logically, a case with no associated values “holds” a Void associated value (singleton type), or not (nil) if the instance has another case.

usage:

let contact = Contact.phone(countryCode: "44", number: "078906789")
let phone = contact.phone.map { $0.countryCode + " " + $0.number } ?? "<No Phone>"     // "44 078906789"

let resolveEmail: KeyPath<Contact, String?> = \Contact.email    // passing contact will resolve to `nil`,
                                                                // but passing something with email will resolve to the addrees

Setter Prisms also produce setters. In that case, if the enum case has an associated value and you want to change the values in the tuple, that is possible as long as the instance points to the same case, otherwise it will be ignored. For example:

var contact = Contact.phone(countryCode: "44", number: "078906789")
contact.phone = (countryCode: "44", number: "99999999")     // ✅ this change happens with success
contact.email = "[email protected]"                              // ? this change is ignored, because the enum instance points to phone, not email

The setter can be really useful if you have a long tree of enums and want to change the leaf. It’s also useful for WritableKeyPath situations.

Extra:

  • Use Prism in the enum if you want to generate code for every case
  • Use PrismCase in a case if you want a different visibility only for that case generated code.
  • Use only PrismCase without Prism in the enum if you want code generated only for that case.
  • Use NoPrism in a case if you don’t want code generated for that case.

PrismCase

A macro that produces predicates and prisms for a single case of an Enum.

Example of predicates:

enum Color {
    case red, black
    @PrismCase
    case green, blue
    case yellow, white
}

produces:

extension Color {
    var isGreen: Bool {
        if case .green = self { true } else { false }
    }
    var isBlue: Bool {
        if case .blue = self { true } else { false }
    }
}

usage:

let color1 = Color.green
color1.isGreen // true
color1.isBlue // false
color1.isRed ? // Compiler error, not generated

Example os prism:

enum Contact {
    case email(address: String)
    @PrismCase
    case phone(countryCode: String, number: String)
    case letter(street: String, house: String, postalCode: String, city: String, state: String, country: String)
    case noContact
}

produces:

extension Contact {
    var phone: (countryCode: String, number: String)? {
        guard case let .phone(countryCode, number) = self else { return nil }
        return (countryCode: countryCode, number: number)
    }
}

Please notice that the Void case is important not only for consistency, but for more advanced cases of composition. Logically, a case with no associated values “holds” a Void associated value (singleton type), or not (nil) if the instance has another case.

usage:

let contact = Contact.phone(countryCode: "44", number: "078906789")
let phone = contact.phone.map { $0.countryCode + " " + $0.number } ?? "<No Phone>"     // "44 078906789"

let resolveEmail: KeyPath<Contact, String?> = \Contact.phone?.number    // passing contact will resolve to `"078906789"`,
                                                                        // but passing something with email will resolve to nil

NoPrism

A macro that prevents the code generatio of predicates and prisms for a specific case, in an Enum marked with Prism

Example of predicates:

@Prism
enum Color {
    case red, green, blue
    @NoPrism
    case white, black
}

produces:

extension Color {
    var isRed: Bool {
        if case .red = self { true } else { false }
    }
    var isGreen: Bool {
        if case .green = self { true } else { false }
    }
    var isBlue: Bool {
        if case .blue = self { true } else { false }
    }
}

usage:

let color1 = Color.red
color1.isRed // true
color1.isGreen // false
color1.isBlue // false
color1.isWhite ? // Compiler error, not generated

Example os prism:

@Prism
enum Contact {
    case email(address: String)
    case phone(countryCode: String, number: String)
    @NoPrism
    case letter(street: String, house: String, postalCode: String, city: String, state: String, country: String)
    @NoPrism
    case noContact
}

produces:

extension Contact {
    var email: String? {
        guard case let .email(address) = self else { return nil }
        return address
    }
    var phone: (countryCode: String, number: String)? {
        guard case let .phone(countryCode, number) = self else { return nil }
        return (countryCode: countryCode, number: number)
    }
}

Please notice that the Void case is important not only for consistency, but for more advanced cases of composition. Logically, a case with no associated values “holds” a Void associated value (singleton type), or not (nil) if the instance has another case.

usage:

let contact = Contact.phone(countryCode: "44", number: "078906789")
let phone = contact.phone.map { $0.countryCode + " " + $0.number } ?? "<No Phone>"     // "44 078906789"

let resolveEmail: KeyPath<Contact, String?> = \Contact.email    // passing contact will resolve to `nil`,
                                                                // but passing something with email will resolve to the addrees

GitHub

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