how to override HashMap#set ? ```class JsonObject ...

# announcements

[tateisu]

how to override HashMap#set ?

class JsonObject : HashMap<String,Any?>() {
    // <https://stackoverflow.com/questions/5525795/does-javascript-guarantee-object-property-order/38218582#38218582>
    // ES2015 require keep insertion order
    private val list = ArrayList<String>()

    // ERROR: set override nothing
     operator override fun set(key: String, value: Any?) {
        super.set(key,value)
        if(!list.contains(key)) list.add(key)
    }

[StavFX]

set is not a method of Map or HashMap, it’s an extension method from stdlib.
You should override put

[tateisu]

oh, thanks

[Dominaezzz]

What's the use-case for extending HashMap btw?

[tateisu]

https://stackoverflow.com/questions/5525795/does-javascript-guarantee-object-property-order/38218582

[Dominaezzz]

LinkedHashMap preserves insertion order. So you can just do class JsonObject : MutableMap<String, Any?>(linkedHashMapOf()).

[tateisu]

hm

[aoriani]

But should your JsonObject be a Map , or should it use a Map ? (Composition over Inheritance)

[StavFX]

Just making a compiling version of what Dominic said:

class JsonObject : MutableMap<String, Any?> by LinkedHashMap()

But you should consider Andre’s question.

[Dominaezzz]

Oops, that's what I meant. I should get some sleep.

[StavFX]

And one last thing to consider, depending on your use-case. If all you wanted was a Map that guarantees order, maybe just use LinkedHashMap directly without extending it?
Or maybe just a typealias for convenience?

typealias JsonObject = LinkedHashMap<String, Any?>

[tateisu]

ES2015 has more rules to object enumeration. I have to override some methods.