Given Kotlin's list lookup syntax,
if (x in myList)
as opposed to idiomatic Java,
if (myList.contains(x))
how can one express negation? The compiler doesn't like either of these:
if (x not in mylist)
if !(x in mylist)
除了if !(mylist.contains(x)))之外，还有其他惯用的表达方式吗？我没看到Kotlin Control Flow docs.人中提到过
Use x !in list syntax.
以下代码:
val arr = intArrayOf(1,2,3)
if (2 !in arr)
println("in list")
被编译成相当于:
int[] arr = new int[]{1, 2, 3};
// uses xor since JVM treats booleans as int
if(ArraysKt.contains(arr, 2) ^ true) {
System.out.println("in list");
}
in和!in运算符使用任何名为contains并返回Boolean的可访问方法或扩展方法.对于集合(List，Set.)，它使用collection.contains方法.对于数组(包括基元数组)，它使用实现为indexOf(element) >= 0的扩展方法Array.contains