if表达式可实现赋值操作：
val z = if (condition) x else y
when表达式代替switch/case
when (x){
1 -> print("x == 1")
2 -> print("x == 2")
else -> {
print("I'm a block")
print("x is neither 1 nor 2")
}
}
val result = when (x) {
0, 1 -> "binary"
else -> "error"
}
when(view) {
is TextView -> view.setText("I'm a TextView")
is EditText -> toast("EditText value: ${view.getText()}")
is ViewGroup -> toast("Number of children: ${view.getChildCount()} ")
else -> view.visibility = View.GONE
}
val cost = when(x) {
in 1..10 -> "cheap"
in 10..100 -> "regular"
in 100..1000 -> "expensive"
in specialValues -> "special value!"
else -> "not rated"
}
val res = when{
x in 1..10 -> "cheap"
s.contains("hello") -> "it's a welcome!"
v is ViewGroup -> "child count: ${v.getChildCount()}"
else -> ""
}
Range 表达式使用一个 .. 操作符，它是被定义实现了一个 RangTo 方法。Ranges 帮助我们使用很多富有创造性的方式去简化我们的代码。比如我们可以把它：
if(i >= 0 && i <= 10) println(i)
转化成：
if (i in 0..10) println(i)
