Is there any use of a mutable extension property i...

# getting-started

[David Kubecka]

Is there any use of a mutable extension property if that property doesn't have a backing field? I.e. is there any way how I can set the value of the property and then retrieve it later via get()?

[Sam]

Well, if you don't have a backing field, you need somewhere else to store the value. A MutableMap would work.

var Foo.bar: String
  set(value) { bars[this] = value }
  get() = bars[this]!!

private val bars = mutableMapOf<Foo, String>()

[David Kubecka]

I see. I've also found a more elaborate answer: https://stackoverflow.com/questions/70630421/kotlin-implement-extension-var-property.

tl;dr: Use WeakHashMap

[Youssef Shoaib [MOD]]

See also https://discuss.kotlinlang.org/t/you-can-apparently-add-state-to-classes-with-extension-properties-with-almost-no-overhead-a-k-a-mixins-in-kotlin/15312/8
Be warned, I wrote this years back