Add function delegation proposition

[MarcinMoskala]

This is just an idea now, but I would like to know what do you think about it

[JakeWharton]

Did you mean "memoize"?

[MarcinMoskala]

You are right, memoize is a better name for this function

[damianw]

This is a better and more general solution -- there's no reason that the rest of the above proposal couldn't be implemented using such operator functions on KFunction[X]. I feel like the proposal can just be reduced to support of something like operator fun functionDelegate(thisRef: Any?, function: KFunction<*>, vararg arguments: Any?). I'd like to see this idea expanded upon... especially the arguments part.

[MarcinMoskala]

Fact is that would be more coherent with property delegation, and I can also make extension functions that would allow previous use-cases:

fun (()->Unit).functionDelegate(thisRef: Any?, function: KFunction<*>) = this()

fun <T1> ((T1)->Unit).functionDelegate(thisRef: Any?, function: KFunction<*>, arg1: T1) = this(arg1)

fun <T1, T2> ((T1, T2)->Unit).functionDelegate(thisRef: Any?, function: KFunction<*>, arg1: T1, arg2: T2) = this(arg1, arg2)

But I would l would like to hear whar others are thinking about it.

[artem-zinnatullin]

To make comparison fair I'd convert that to expression body:

override fun deleteListElementAt(position: Int) = adapter.deleteAt(position)

[MarcinMoskala]

It changes nothing, and I am not using single expression functions for expressions that are returning Unit because this is misleading for a person who is reading it.

[artem-zinnatullin]

It changes nothing

Current example takes 3 lines of code without delegate, with delegate it takes 1. But in simple cases delegate only omits function arguments in compare to expression body =.

and I am not using single expression functions for expressions that are returning Unit because this is misleading for a person who is reading it.

• In your own examples delegate hides return type Unit as well: override fun deleteListElementAt(position: Int) by adapter::deleteAt
• You can always specify return type explicitly if you want override fun deleteListElementAt(position: Int): Unit = adapter.deleteAt(position)

Just want to remove bias from the syntax comparison, so far I'm positive about this proposal :)

[MarcinMoskala]

Sound fair. I will change it then

[artem-zinnatullin]

override fun setTitle(text: String) = titleView.setText(text)

[MarcinMoskala]

It changes nothing, and I am not using single expression functions for expressions that are returning Unit, because this is misleading for a person who is reading it.

[artem-zinnatullin]

Would be great to explicitly cover contructor delegation in the proposal!

Could be super helpful for boilerplate reduction in DI/factory functions:

@Module
class DeviceModule {
  
  @Provides
  fun motherboard(cpu: Cpu, ram: Ram, gpu: Gpu): Motherboard by ::RealMotherboard
}

[d3xter]

Will it be possible to use an arbitrary expression to delegate to, or just an existing function?

If arbitrary expressions are allowed, that proposal would make the "Pointfree" style (Haskell Pointfree) possible:

infix fun <T, R, S> ((T) -> R).compose(f: (R) -> S) : (T) -> S = { f(this(it)) }

fun add5(i: Int) = i + 5

fun add10(i: Int) = i + 10

fun stringToInt(s: String) = s.toInt()

fun convertAndAdd15 by ::stringToInt compose ::add5 compose ::add10