Cici's notebook

[] 的用途就是 用索引（index）去取得或設定值：

a[0] → 取得 index = 0 的值

a[0] = 10 → 設定 index = 0 的值

Kotlin 將這個行為對應到：

operator fun get(index: ...)
operator fun set(index: ..., value: ...)

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class MyMap {
    private val map = mutableMapOf<String,String>()
    operator fun get(key:String) : String {
        return map[key] ?: ""
    }
    operator fun set(key:String, value: String) {
        map[key] = value
    }
}
fun main() {
    val myMap = MyMap()
    myMap["name"] = "alice"
    println("name = ${myMap["name"]}")
    myMap["address"] = "Taiwan"
    println("address = ${myMap["address"]}")
}

name = alice
address = Taiwan

其它運算子

運算子 覆寫方法 說明
[] get/set 索引
in contains 是否包含
== equals 比較
() invoke 呼叫
.. rangeTo 區間

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