How can I programmatically make methods chainable?

Question

Let\'s say I have a class and I want to make its methods chainable, I could do something like this:

class MyClass {

  def methodOne(arg1: Any): MyClass = {
             


        

Answer 1

Leaving aside the question of how wise this is in the first place, it's pretty easy to implement in a type-safe and boilerplate-free way with Shapeless:

import shapeless._

trait ChainableUtils {
  def makeChainable[F, Args <: HList](f: F)(implicit
    in: FnHListerAux[F, Args => Unit],
    out: FnUnHLister[Args => this.type]
  ) = out((a: Args) => { in(f)(a); this })
}

And then:

scala> class MyClass extends ChainableUtils {
     |   def func1 = makeChainable((i: Int) => println("Doing stuff."))
     |   def func2 = makeChainable((a: Any, b: Any) => 
     |     println("Doing other stuff."))
     | }
defined class MyClass

scala> val myInstance = new MyClass
myInstance: MyClass = MyClass@6c86b570

scala> myInstance.func1(1).func2('a, "a").func1(42)
Doing stuff.
Doing other stuff.
Doing stuff.
res0: myInstance.type = MyClass@6c86b570

This will work for any FunctionN.