`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`

This kinda works but it is not thread safe ``` class LazyExtension lt V T gt val f V gt T data class Result lt T gt val t T var result Result lt T gt = null operator fun getValue thisRef V property kotlin reflect KProperty lt gt T return result t Result thisRef f also result = it t ```

`val A extVal get = B this ` Is there a way to not construct kotlinlang #announcements

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Title

edwardwongtl

09/19/2017, 8:39 AM

val A.extVal get() = B(this)

Is there a way to not construct

every time I reference to

A.extVal

? Given that I don't own class

marstran

09/19/2017, 9:06 AM

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.

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

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
    }
}

👍 2

edwardwongtl

09/19/2017, 10:22 AM

Wow thanks man, I will take a look

marstran

09/19/2017, 10:49 AM

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

tmp

variable.

ilya.gorbunov

09/19/2017, 10:52 AM

@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

09/19/2017, 10:54 AM

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

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

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