android - Why isn't myDayForecast.map empty?

Question

I create a object myDayForecast with secondary construction, I think the var bb will be empty because the parmater of secondary construction which pass to main construction is HashMap(). I see some document about HashMap(), it will return empty.

But after I run the code, I find the var bb isn't empty (You can see image), why?

var myDayForecast= DayForecast(15L,"Desciption",10,5,"http://www.a.com",10L)
var bb=myDayForecast.map

class DayForecast(var map: MutableMap<String, Any?>) {
    var _id: Long by map
    var date: Long by map
    var description: String by map
    var high: Int by map
    var low: Int by map
    var iconUrl: String by map
    var cityId: Long by map

    constructor(date: Long, description: String, high: Int, low: Int, iconUrl: String, cityId: Long)
            : this(HashMap()) {
        this.date = date
        this.description = description
        this.high = high
        this.low = low
        this.iconUrl = iconUrl
        this.cityId = cityId
    }
}

Result Image

Answer 1

You're using a map to store your property data in it. This is done via by map and works for getting and setting. By assigning a value to the properties you add elements to the map. So initially your HashMap is empty, but at the end of the constructor, you've added values to it implicitly. Kotlin doesn't create another field or mechanism to store the values otherwise.