try-with-resources / use / multiple resources

Question

I\'m using a Java-API which heavily uses the Autoclosable-Interface and thus in Java try-with-resources. However in Java you can specify

Answer 1

For simplicity I will use A,B and C for the chained autocloseables.

import java.io.Closeable

open class MockCloseable: Closeable {
    override fun close() = TODO("Just for compilation")
}
class A: MockCloseable(){
    fun makeB(): B = TODO()
}
class B: MockCloseable(){
    fun makeC(): C = TODO()

}
class C: MockCloseable()

Using uses

This would look like this:

A().use {a ->
    a.makeB().use {b -> 
        b.makeC().use {c -> 
            println(c)
        }
    }
}

Making a chain use function with a wrapper

Definition

class ChainedCloseable(val payload: T, val parents: List) {
    fun  use(block: (T)->U): U {
        try {
            return block(payload)
        } finally {
            payload.close()
            parents.asReversed().forEach { it.close() }
        }
    }

    fun  convert(block: (T)->U): ChainedCloseable {
        val newPayload = block(payload)
        return ChainedCloseable(newPayload, parents + payload)
    }
}

fun  T.convert(block:(T)->U): ChainedCloseable {
    val new = block(this)

}

Usage

A()
    .convert(A::makeB)
    .convert(B::makeC)
    .use { c ->
         println(c)
    }

This allows you to avoid having to nest deeply, at the cost of creating wrapper objects.