Generics 科特林的安全流畅演员?
具有以下扩展功能:Generics 科特林的安全流畅演员?,generics,kotlin,casting,fluent,Generics,Kotlin,Casting,Fluent,具有以下扩展功能: inline fun <reified OUT> Any.cast(): OUT = this as OUT inline fun <reified IN, reified OUT: IN> IN.downcast(): OUT = this as OUT inline fun <reified IN: OUT, reified OUT> IN.upcast(): OUT = this as OUT 这就是我所说的括号地狱。通过语法,我试
inline fun <reified OUT> Any.cast(): OUT = this as OUT
inline fun <reified IN, reified OUT: IN> IN.downcast(): OUT = this as OUT
inline fun <reified IN: OUT, reified OUT> IN.upcast(): OUT = this as OUT
这就是我所说的括号地狱。通过语法,我试图实现以下目标(不安全的强制转换版本):
source.cast().someField.cast().someField.cast().someField.cast().desiredField
虽然它不是一个较短的语法,但可读性更高,并且没有括号地狱。问题是,我以这种方式丢失了类型检查,因此我可能会编写“abc”.cast()
,并导致异常
我如何才能使这更安全,并保持流畅的语法?您将术语“向上播放”和“向下播放”颠倒过来。向下转换(转换为子类)本质上是不安全的。使用泛型方法可以防止您意外地强制转换到不可能是子类的对象,但是由于您必须检查合格性以确保安全,因此我不认为使用泛型方法是值得的。向上转换(转换为超类)是多余的,所以不需要函数。@Tenfour04。是的,我上下都搞砸了:我加上了向上投射只是为了完整性。
val x1: Number = 42
val x2: String = "abc"
val x3: Double = 3.14
val y1: Int = x1.downcast<Number, Int>()
val y2: CharSequence = x2.upcast<String, CharSequence>()
val y3: Float = x3.cast<Float>() // dangerous, crash
x1.downcast<Number, Int>()
x1.downcast<Int>()
interface A1Able
class B1Impl : A1Able { val desiredField = 42 }
class C1Impl : A1Able
interface A2Able
class B2Impl : A2Able { val someField: A1Able = C1Impl() }
class C2Impl : A2Able { val someField: A1Able = B1Impl() }
interface A3Able
class B3Impl : A3Able { val someField: A2Able = C2Impl() }
class C3Impl : A3Able { val someField: A2Able = B2Impl() }
interface A4Able
class C4Impl : A4Able { val someField: A3Able = B3Impl() }
fun main() {
val source: A4Able = C4Impl()
val desiredField = ((((source as C4Impl).someField as B3Impl).someField as C2Impl).someField as B1Impl).desiredField
}
source.cast<C4Impl>().someField.cast<B3Impl>().someField.cast<C2Impl>().someField.cast<B1Impl>().desiredField