backing fieldのgetでCloseしないといけないリソースを返して、そいつをuseしたときにitで新たなリソースが生成されないことを確認する

backing_field_practice.kt

import java.io.Closeable

class Resource: Closeable {
    init {
    	println("resource ref +1")        
    }
    
    fun play() {
        println("play")
    }
    
    override fun close() {
        println("resource ref -1")
    }
}

class Practice {
    private val resource
    	get() = Resource()
    
    fun execute() {
        resource.use {
            it.play()
        }

        resource.use {
            resource.use {
                it.play()
                it.play()
            }

            resource.use {
                it.play()
                it.play()
                it.play()
            }
        }
    }
}

fun main(args: Array<String>) {
    Practice().execute()
}

実行結果

resource ref +1
play
resource ref -1
resource ref +1
resource ref +1
play
play
resource ref -1
resource ref +1
play
play
play
resource ref -1
resource ref -1