How does Class not inherit some variables? - swift

Question

class Model {
let userId: Int
let username: String
private let description: String?
init(userId: Int, username: String, description: String?) {
self.userId = userId
self.username = username
self.description = description
}
}
class ModelDetail: Model {
let url: String
let detail: String
init(url: String, detail: String, userId: Int, username: String, description: String?) {
self.url = url
self.detail = detail
super.init(userId: userId, username: username, description: description)
}
}
I prepared this sample code to copy here. I don't want to inherit "description" value from Model class. When I try to something I am getting this error: Missing argument for parameter 'description' in call
Is it possible not to inherit some variable?

Answer 1

You cannot not inherit description, but you can assign a value nil to it, and simply ignore it.
If you can modify Model, you can change its init to
class Model {
// ...
init(userId: Int, username: String, description: String? = nil)
// ...
}
Since description is optional, we set it to nil by default, so ModelDetail doesn't need to set it at all:
class ModelDetail: Model {
let url: String
let detail: String
init(url: String, detail: String, userId: Int, username: String) {
self.url = url
self.detail = detail
super.init(userId: userId, username: username)
}
}
If you cannot change Model, then ModelDetail can invoke Model's init with nil for description:
class ModelDetail: Model {
// ...
init(url: String, detail: String, userId: Int, username: String) {
// ...
super.init(userId: userId, username: username, description: nil)
}
}
If you want to strictly adhere to the inheritance rules (which do not allow for "unused" fields), then you need to separate description from the model ModelDetail will be inheriting from. I.e.:
Have a base model, which only has userId and username
Both Model and ModelDetail will inherit from that base model, rather than each other:
class BasicModel {
let userId: Int
let username: String
init(userId: Int, username: String) {
self.userId = userId
self.username = username
}
}
class Model: BasicModel {
private let description: String?
init(userId: Int, username: String, description: String?) {
self.description = description
super.init(userId: userId, username: username)
}
}
class ModelDetail: BasicModel {
let url: String
let detail: String
init(url: String, detail: String, userId: Int, username: String) {
self.url = url
self.detail = detail
super.init(userId: userId, username: username)
}
}