Swift-structures 和 classes 初始化

structure

1. memberwise initializer

　　1.1 不需要default values和intializer

///-------------------------- structures --------------------------///
// only structures automatically generate a memberwise initializer
// don't need default values and initializer
struct StructA {
    let propertyA: Int
    let propertyB: Double
}

//------------------ memberwise initializer ----------------//
// the memberwise initializer works well
let a = StructA(propertyA: 1, propertyB: 1.0)

　　1.2 使用memberwise initializer注意参数的顺序，memberwise initializer的参数列表是自动镜像存储属性列表的，举例：

// the memberwise initializer doesn't work
// the automatic memberwise initializer argument list's order mirrors that of the stored property list
let b = StructA(propertyB: 1.0, propertyA: 1)

　　1.3 如果属性已经有default value，则

struct StructA {
    let propertyA: Int = 1
    let propertyB: Double
}

let aa = StructA(propertyB: 1.0)

　　此时是不能 let aa = StructA(propertyA: 1, propertyB: 1.0) 的

　　如果想要，可以这么做，如下

2. 等价的 initializer

//equivalent initializer
extension StructA {
    init(propertyB: Double) {
        self.propertyB = propertyB
    }
}
// works well
let ab = StructA(propertyA: 1, propertyB: 1.0)

3. 添加default value

//-------------------------- custom initializer --------------------------//

init(propertyA: Int = 1, propertyB: Double = 1.0) {
    // 处理初始值
}