is and !is 操作符
is和!is可以用来检查一个实例是否属于一种类型
if (obj is String) {
print(obj.length)
}
if (obj !is String) { // same as !(obj is String)
print("Not a String")
}
else {
print(obj.length)
}
Kotlin里经过is检查的变量不用显示的转型（自动转换）
fun demo(x: Any) {
if (x is String) {
print(x.length) // x is automatically cast to String
}
}
或者
if (x !is String) return
print(x.length) // x is automatically cast to String
或者
&& 和 || 的右边
// x is automatically cast to string on the right-hand side of `||`
if (x !is String || x.length == 0) return
// x is automatically cast to string on the right-hand side of `&&`
if (x is String && x.length > 0) {
print(x.length) // x is automatically cast to String
}
或者when里
when (x) {
is Int -> print(x + 1)
is String -> print(x.length + 1)
is IntArray -> print(x.sum())
}
如果变量check和usage之间，编译器无法保证变量不变，则不会做自动转换
- val local variable
- val properties
- var local variable
- var properties
as操作符
通过as转型失败时会抛出异常，as？转型失败会返回null
val x: String = y as String
val x: String? = y as? String
