演算子オーバーロード Ruby Kotlin class Id(val int: Int) { operator fun plus(that: Id) = Id(this.int + that.int) } val id1 = Id(1) val id2 = Id(2) println(id1 + id2) class Id attr_reader :int def initialize(int) @int = int end def +(that) Id.new(@int + that.int) end end id1 = Id.new(1) id2 = Id.new(2) p id1 + id2