How to preserve a struct memberwise initializer when you have a custom initializer

In the previous article, I talk about Memberwise Initializers, which you get for free on structure types if you don't define any custom initializers.

There might be a time where you want to have a custom initializer, but you don't want to lose memberwise initializer.

Extension

To preserve a memberwise initializer, you can declare a custom initializer in an extension.

struct User {
    let firstName: String
    let lastName: String
}

extension User {
    init(fullName: String) {
        let components = fullName.components(separatedBy: " ")
        firstName = components[0]
        lastName = components[1]
    }
}

The above User struct will got two initializers, User(firstName: String, lastName: String) and User(fullName: String).

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Explicit conformance

Another use case is when you have explicit conformance to Codable protocol.

struct User: Codable {
    let firstName: String
    let lastName: String

    init(from decoder: Decoder) throws {
        ...
    }
}

The above code will remove a memberwise initializer since you declare a custom initializer. You can conform to Codable protocol in an extension and declare a custom initializer there to preserve a memberwise initializer.

struct User {
    let firstName: String
    let lastName: String
}

extension User: Codable {
    init(from decoder: Decoder) throws {
        ...
    }
}

If you don't need special care in init(from decoder: Decoder) throws, you can conform to it normally and get both memberwise initializer, and the one generated from Codable.

struct User: Codable {
    let firstName: String
    let lastName: String
}

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Related Resources

• Memberwise Initializers for Structure Types