考虑以下示例代码:
import Foundation
protocol StringInitable {
init( string:String )
}
class A : StringInitable {
var stored:String
required init ( string:String ) {
stored = string
}
}
class B : A /*, StringInitable */ {
var another_stored:String
required init ( string:String ) {
another_stored = "B-store"
super.init(string: string)
}
}
func maker<T:StringInitable>(string:String) -> T {
return T(string: string)
}
let instanceA = A(string: "test-maker-A")
let instanceB = B(string: "test-maker-B")
let makerA:A = maker("test-maker-A")
let makerB:B = maker("test-maker-B")
let typeInstanceA = _stdlib_getTypeName(instanceA)
let typeMakerA = _stdlib_getTypeName(makerA)
let typeInstanceB = _stdlib_getTypeName(instanceB)
let typeMakerB = _stdlib_getTypeName(makerB)
从结果来看,编译器似乎已经推断出了正确的类型,但是未能调用正确的初始值设定项。为什么我必须在B类中显式实现StringInitable(尝试将B类定义中的注释删除)才能让通用函数“ maker”调用正确的初始化程序?