Kotlin needs try-with-resources

Language Design
54

Here’s a simple implementation (Be sure to try running and editing it right in the forum!):

class ResourceScope {
    private val resources = mutableListOf<AutoCloseable>()
    
    fun close() {
        // In this case I chose to close with first-in-first-out.
        // You could always extend this class to enable other kinds of closing strategies.
        resources.forEach { it.close() } 
    }
    
    fun AutoCloseable.autoClose() { 
        resources += this 
    }
}

fun using(block: ResourceScope.() -> Unit) {
    val rs = ResourceScope()
    try {
        rs.block()
    } finally {
        rs.close()
    }
}

fun main() {
//sampleStart
    using {
        val myResource = ExampleClosable("myResource").autoClose()
        for (i in 0..5) {
            ExampleClosable("$i").autoClose()
        }
        // error("Triggered error!") // Try uncommenting this to see that no resources are left un-closed.
        println("Success!")
    }
//sampleEnd
}

class ExampleClosable(val name: String) : AutoCloseable {
    init {
        println("Created resource $name")
    }
    override fun close() = println("Closing $name")
}

I’m sure there will be plenty of ways to improve on it. Like mentioned earlier in this thread, the ResourceScope (others used ResourceHolder) could be configured to handle resources in different ways allowing interesting solutions.