polish context-receivers.md

[Serendipithub]

• Conveniently scoping automatically closeable resources (flexible “try-with-resources”)

interface AutoCloseScope {
    fun defer(closeBlock: () -> Unit) //there be defer
}

context(AutoCloseScope)
fun File.open(): InputStream

fun withAutoClose(block: context(AutoCloseScope) () -> Unit) {
    val scope = AutoCloseScopeImpl() // Not shown here
    try {
        with(scope) { block() }
    } finally {
        scope.close()  //there be close
    }   
}

// usage
withAutoClose {
    val input = File("input.txt").open()
    val config = File("config.txt").open()
    // Work
    // All files are closed at the end
}

I think the two methods (defer, close) should be the same name for easier understanding.

[elizarov]

That's just an example of how it might be used, not a polished design. Anyway, those two methods cannot have the same name, since they do completely different things -- defer registers a block to be called on close, while close calls all the blocks registered by defer. They might share some elements of their name, though.