data class Customer(val name: String, val email: String)

fun foo(a: Int = 0, b: String = "") {...}

val positives = list.filter { x -> x >0 }

val positives = list.filter { it > 0 }

println("Name $name")

when (x) {is Foo ->  ...is Bar -> ...else -> ...
}

for ((k, v) in map) {print("$k -> $v")
}

for (i in 1..100) { ... }  // 闭区间: 包括100
for (i in 1 until 100) { ... } // 半开区间: 不包括100
for (x in 2..10 step 2) { ... }
for (x in 10 downTo 1) { ... }
if (x in 1..10) { ... }
for (i in 1..100) { ... }
for (i in 2..10) { ... }

val p: String by lazy {// 生成string的值
}

fun String.spcaceToCamelCase() { ... }
"Convert this to camelcase".spcaceToCamelCase()

object Resource {val name = "Name"
}

val files = File("Test").listFiles()
println(files?.size)

val files = File("test").listFiles()
println(files?.size ?: "empty")

val data = ...
val email = data["email"] ?: throw IllegalStateException("Email is missing!")

val date = ...
data?.let{...//如果不为空执行该语句块
}

fun transform(color: String): Int {return when(color) {"Red" -> 0"Green" -> 1"Blue" -> 2else -> throw IllegalArgumentException("Invalid color param value")}
}

fun test() {val result = try {count()}catch (e: ArithmeticException) {throw IllegaStateException(e)}//处理 result
}

fun foo(param: Int){val result = if (param == 1) {"one"} else if (param == 2) {"two"} else {"three"}
}

fun arrOfMinusOnes(size: Int): IntArray{return IntArray(size).apply{ fill(-1) }
}

fun theAnswer() = 42

fun theAnswer(): Int {return 42
}

fun transform(color: String): Int = when (color) {"Red" -> 0"Green" -> 1"Blue" -> 2else -> throw IllegalArgumentException("Invalid color param value")
}

class Turtle {fun penDown()fun penUp()fun turn(degrees: Double)fun forward(pixels: Double)
}
val myTurtle = Turtle()
with(myTurtle) { // 画一个100像素的正方形penDown()for(i in 1..4) {forward(100.0)turn(90.0)}penUp()
}

val stream = Files.newInputStream(Paths.get("/some/file.txt"))
stream.buffered().reader().use { reader ->println(reader.readText())
}

//  public final class Gson {//     ...
//     public <T> T fromJson(JsonElement json, Class<T> classOfT) throws JsonSyntaxException {//     ...inline fun <reified T: Any> Gson.fromJson(json): T = this.fromJson(json, T::class.java)

val b: Boolean? = ...
if (b == true) {...
} else {// `b` 是false或者null
}