I've created separate swift files for to keep things separate

Models.swift

// OrderRepresentable.swift
protocol OrderRepresentable {
    var name: String { get }
    var description: String { get }
    var price: Int { get }
}

// Order.swift
struct Order: OrderRepresentable {
    var name: String = ""
    var description: String = ""
    var price: Int = 0
    
    init(name: String, description: String, price: Int) {
        self.name = name
        self.description = description
        self.price = price
    }
}

// CompletedOrder.swift
struct CompletedOrder: OrderRepresentable {
    var name: String = ""
    var description: String = ""
    var price: Int = 0
    var completedDate: String = ""
    var userRating: Double = 4.5
    
    init(name: String, description: String, completedDate: String, userRating: Double, price: Int) {
        self.name = name
        self.description = description
        self.completedDate = completedDate
        self.userRating = userRating
        self.price = price
    }
}