我有一个名为 Parameter
的协议:
protocol Parameter {
var name: String { get }
var unit: Unit? { get }
var value: Double { get }
init(name: String, unit: Unit?, value: Double)
}
我还有16个符合 Parameter
的结构:
struct Calcium: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Calcium", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Alkalinity: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Alkalinity", unit: Unit? = Unit(symbol: "ppm CaCO3"), value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Salinity: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Salinity", unit: Unit? = Unit(symbol: "SG"), value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Temperature: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Temperature", unit: Unit? = UnitTemperature.fahrenheit, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct PH: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "pH", unit: Unit? = nil, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Magnesium: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Magnesium", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Phosphate: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Phosphate", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Ammonia: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Ammonia", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Silica: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Silica", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Iodine: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Iodine", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Nitrate: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Nitrate", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Nitrite: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Nitrite", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Strontium: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Strontium", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct ORP: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "ORP", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Boron: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Boron", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
struct Iron: Parameter {
var name: String
var unit: Unit?
var value: Double
init(name: String = "Iron", unit: Unit? = UnitDispersion.partsPerMillion, value: Double) {
self.name = name
self.unit = unit
self.value = value
}
}
如您所见,所有结构都实现了相同的初始化程序 . 在初始化程序中,我为 Parameter
协议所需的三个参数中的两个提供默认值,这为我提供了以下初始化程序:
let calcium = Calcium(value: Double)
我还获得了结构创建的默认初始值设定项:
let calcium = Calcium(name: String, unit: Unit?, value: Double)
当我创建结构的实例时,两个初始值设定项都出现在Xcode 's code completion popover. However, I don'中,希望 name
和 unit
参数能够与初始化程序中提供的默认值不同 . 我还尝试为 name
和 unit
属性分配默认值,它们在结构内部声明,但在 Parameter
协议所需的初始化程序之外 .
有没有办法通过为 name
和 unit
参数提供默认值来初始化结构,只需要提供 value
参数,而没有在Xcode的代码完成弹出窗口中显示默认初始值设定项?
我在Xcode 's code completion popup is that I don'中出现两个初始值设定项时唯一需要关注的是其他人创建结构并提供除了我在 Parameter
协议所需的初始化程序中提供的值之外的值 .
我意识到我可以用一个类来完成,但我试图通过面向协议的编程和使用结构来使我的思想正确 .
1 回答
一种方法:
我们将所有变量更改为选项,并使用协议中的默认参数删除了初始化程序 . 如果
unit
和value
将始终具有默认值,则客户端无需查看此初始化程序 .并将结构更改为如下所示:
在结构本身,我们添加了私有初始化程序,它从只需要一个参数的自定义初始化程序调用 .
并且您将在Xcode完成弹出窗口中只有一个初始化程序 .