Another question that I have. What is the recommen...

# arrow

[Clarence Dimitri Charles]

Another question that I have. What is the recommended way of doing dependency injection ? Based on my research, there is the Reader monad based on a article written by Jorge Castillo. There is also this

talk▾

with Francisco Garcia. And also in the arrow documentation, you can do it using Typeclass. What is the recommended way of doing dependency injection ? what are the advantages of one method over the other ? If this question is not asked to the right channel, feel free to redirect me to the correct one

[pakoito]

Reader is a more general technique that comes with a runtime cost, and some boilerplate.

The other one takes extension functions and makes them into DI elements. It takes a bit more brainpower to get right, and comes without a runtime penalty.

Both approaches are purely functional. You still have the global injector frameworks like coin and dagger, depending on how much magic and coupling you'd like in your app.

[stojan]

here is one approach with Extension functions in a gist by @raulraja https://gist.github.com/raulraja/97e2d5bf60e9d96680cf1fddcc90ee67

[Satyam Agarwal]

@pakoito what is the runtime cost for reader ?

[pakoito]

You're wrapping and unwrapping into a Reader, even if you have no effects or...either, it'll be Id, which is just regular boxing.

[pakoito]

fun Int.thing(): Int = this

fun thing(): Reader<Int, Int> = Reader {
  ask()
}

[Satyam Agarwal]

Right. That I’ve notice a lot while using reader.

[simon.vergauwen]

https://gist.github.com/nomisRev/1f91710ebec1709d4ce8059812482624

Here is another example which uses extensions functions to replace Reader, interface delegation to do dependency composition, and uses generic function constraints to define top-level function that can define all there dependencies as non-params.

[Clarence Dimitri Charles]

Ok thx for your useful responses

[HieiJ]

The only limitation I've found using the extension functions solution is with anonymous suspend functions. Or maybe I'm not aware of how to declare them...

[HieiJ]

fun <R : Console> doSomething() {
  val myFunction: suspend R.(i: Int) -> Unit = suspend { i: Int -> print("AAA $i") }

[HieiJ]

(this doesn't compile)

[HieiJ]

(sorry, I was wrong, it can be defined without problems...)

[pakoito]

¿?

[pakoito]

what was the issue?

[HieiJ]

probably that I was too tired... 🤣 anyway, in the past I had some compatibility problems, e.g with List<>.traverse(). I can traverse a List<IO<A>> but not a List<suspend () -> A>, but maybe now it is fixed.

[simon.vergauwen]

but not a List<suspend () -> A>, but maybe now it is fixed.

You can now 😉