Kotlin学习教程之操作符重载详解

data class Point(val x: Int, val y: Int) { operator fun plus(other: Point) = Point(x + other.x, y + other.y) operator fun plus(value: Int) = "toString: ${Point(x + value, y + value)}"}fun main(args: Array<String>) { val p1 = Point(1, 2) val p2 = Point(3, 4) println(p1 + p2) println(p1 + 3)}/*Point(x=4, y=6)toString: Point(x=4, y=5)*/

// 第一个文件：package package0operator fun Point.times(value: Int) = Point(x * value, y * value)// 第二个文件：package package1operator fun Point.times(value: Int) = Unit // Do nothing.// 使用第一个扩展操作符：import package0.timesval newPoint = Point(1, 2) * 3

data class Size(var width: Int = 0, var height: Int = 0) { operator fun plus(other: Size): Size { return Size(width + other.width, height + other.height) } operator fun plusAssign(other: Size) { width += other.width height += other.height }}fun main(args: Array<String>) {// var s1 = Size(1, 2) // 如果这么写，执行 += 时会报错. val s1 = Size(1, 2) val s2 = Size(3, 4) s1 += s2}

fun main(args: Array<String>) { val list = arrayListOf(1, 2) list += 3 // 添加元素到自身集合, 没有新的对象被创建, 调用的是 add 方法. val newList = list + 4 // 创建一个新的 ArrayList, 添加自身元素和新元素并返回新的 ArrayList.}

println("hello" in arrayListOf("hello", ", ", "world"))/*true*/

/** * A range of values of type `Int`. */public class IntRange(start: Int, endInclusive: Int) : IntProgression(start, endInclusive, 1), ClosedRange<Int> { override val start: Int get() = first override val endInclusive: Int get() = last override fun contains(value: Int): Boolean = first <= value && value <= last override fun isEmpty(): Boolean = first > last override fun equals(other: Any?): Boolean = other is IntRange && (isEmpty() && other.isEmpty() || first == other.first && last == other.last) override fun hashCode(): Int = if (isEmpty()) -1 else (31 * first + last) override fun toString(): String = "$first..$last" companion object { /** An empty range of values of type Int. */ public val EMPTY: IntRange = IntRange(1, 0) }}

for (index in 1..10) { // 遍历 1 到 10, 包括 1 和 10.}

/** * Creates a range from this [Comparable] value to the specified [that] value. * * This value needs to be smaller than [that] value, otherwise the returned range will be empty. * @sample samples.ranges.Ranges.rangeFromComparable */public operator fun <T: Comparable<T>> T.rangeTo(that: T): ClosedRange<T> = ComparableRange(this, that)

fun main(args: Array<String>) { val c1 = Calendar.getInstance() // 代表今天. val c2 = Calendar.getInstance()  c2.add(Calendar.DATE, 10) // 代表 10 天后. val c3 = Calendar.getInstance() c3.add(Calendar.DATE, 3) // 代表 3 天后. val c4 = Calendar.getInstance() c4.add(Calendar.DATE, 13) // 代表 13 天后.  // 判断某日期是否在某两个日期范围内. println(c3 in c1..c2) println(c4 in c1..c2)}/*truefalse*/

data class Point(val x: Int, val y: Int)operator fun Point.unaryMinus() = Point(-x, -y)val point = Point(10, 20)println(-point)/*Point(x=-10, y=-20)*/

@Suppress("IMPLICIT_CAST_TO_ANY", "UNCHECKED_CAST")operator fun <T> SharedPreferences.get(key: String, defValue: T) = when (defValue) { is String -> getString(key, defValue) is Int -> getInt(key, defValue) is Long -> getLong(key, defValue) is Float -> getFloat(key, defValue) is Boolean -> getBoolean(key, defValue) else -> throw RuntimeException()} as T@SuppressLint("CommitPrefEdits")operator fun <T> SharedPreferences.set(key: String, value: T) = with(edit()) { when (value) { is String -> putString(key, value) is Int -> putInt(key, value) is Long -> putLong(key, value) is Float -> putFloat(key, value) is Boolean -> putBoolean(key, value) else -> throw RuntimeException() }.apply()}fun main(args: Array<String>) { val version = sp["key_version", 47] // 读 sp. sp["key_version"] = 48 // 写 sp.}

data class Movie(val name: String, val score: Int, val date: Date, val other: Any = Any()) : Comparable<Movie> { override fun compareTo(other: Movie): Int {  return compareValuesBy(this, other, Movie::score, Movie::date, Movie::name) // 如果将 Movie::other 也用作比较会报错, 因为 other 不是 Comparable 类型的。 }}fun main(args: Array<String>) { val df = SimpleDateFormat("yyyy-MM-dd", Locale.getDefault()) val movie0 = Movie("马戏之王", 8, df.parse("2018-01-31")) val movie1 = Movie("神秘巨星", 7, df.parse("2018-01-01")) val movie2 = Movie("移动迷宫", 7, df.parse("2018-01-02")) println(movie0 < movie1) println(movie1 < movie2)}/*falsetrue*/

/** * Compares two values using the specified functions [selectors] to calculate the result of the comparison. * The functions are called sequentially, receive the given values [a] and [b] and return [Comparable] * objects. As soon as the [Comparable] instances returned by a function for [a] and [b] values do not * compare as equal, the result of that comparison is returned. * * @sample samples.comparisons.Comparisons.compareValuesByWithSelectors */public fun <T> compareValuesBy(a: T, b: T, vararg selectors: (T) -> Comparable<*>?): Int { require(selectors.size > 0) return compareValuesByImpl(a, b, selectors)}private fun <T> compareValuesByImpl(a: T, b: T, selectors: Array<out (T)->Comparable<*>?>): Int { for (fn in selectors) {  val v1 = fn(a)  val v2 = fn(b)  val diff = compareValues(v1, v2)  if (diff != 0) return diff } return 0}

class Delegate {  operator fun getValue(thisRef: Any?, property: KProperty<*>): String {    //...  }  operator fun setValue(thisRef: Any?, property: KProperty<*>, value: String) {    //...  }}