`val A.extVal get() = B(this)` Is there a way to n...

# announcements

[edwardwongtl]

val A.extVal get() = B(this)
Is there a way to not construct B every time I reference to A.extVal? Given that I don't own class A.

[marstran]

I tried using the lazy-delegate, but it didn't work because you don't have access to this inside the function you pass to it. I guess you could create your own version of the lazy-delegate that passes the receiver object as a parameter to the function though.

[marstran]

You can read how to do this here: https://kotlinlang.org/docs/reference/delegated-properties.html

[marstran]

This kinda works, but it is not thread safe:

class LazyExtension<V, T>(val f: V.() -> T) {
    data class Result<T>(val t: T)
    var result: Result<T>? = null
    
    operator fun getValue(thisRef: V, property: kotlin.reflect.KProperty<*>): T {
        return result?.t ?: Result(thisRef.f()).also { 
            result = it
        }.t
    }
}

[edwardwongtl]

Wow thanks man, I will take a look

[marstran]

I fixed it up a little bit so it doesn't use that tmp variable.

[ilya.gorbunov]

@marstran Note that this implementation of LazyExtension would return the same value for any receiver after it had been initialized. Probably not what the author wanted.

[marstran]

Ah, that's true. You would also need to keep track of all the receivers.

[marstran]

I guess that could turn out to be quite a memory leak if it is used a lot.