Hello. We have discussion with our colleagues about `also` vs `apply` usages. We have a method that ...

# codingconventions

[david.bilik]

Hello. We have discussion with our colleagues about also vs apply usages. We have a method that needs to return some type but I would like to store instance of returned type to member property, something like

lateinit var view : View
fun createView(context : Context) : View {
  return with(context) {
    view = frameLayout {
    }
  }
}

this example would not compile because return type of view = frameLayout is unit. The variants to solve that are

fun createView(context : Context) : View {
  return with(context) {
    view = frameLayout {
    }
    view
  }
}

fun createView(context : Context) : View {
  return with(context) {
    view = frameLayout {
    }.apply { view = this }
  }
}

fun createView(context : Context) : View {
  return with(context) {
    view = frameLayout {
    }.also { view = it }
  }
}

I prefer the also variant because it seems that this operator was made for this usages “do something also with this expression” and apply is for cases when i would like to modify instance in its context. Any opinions?

[marstran]

I don't think you need to use with here. If frameLayout is a function on Context, you can try this: return context.frameLayout {}.apply { k = this }.

[david.bilik]

Well thats not really a thing I wanted to discuss, this is just an really simple example, in real world the view is much more complicated and usage of with is justifiable.

[gildor]

I don’t see big difference between apply and also in this case.
Probably I would choosy apply

[marstran]

The only difference between apply and also is that apply takes an extension function (so that the parameter is given as this), while also takes a normal function. The also function was added to Kotlin 1.1 to deal with the case where apply would shadow this from the outer scope.

[kirillrakhman]

I would use also, see https://github.com/yole/kotlin-style-guide/issues/35 for my rationale

[Andreas Sinz]

+1 for also. apply sounds like do some stuff on foo, while also sounds like do something else with foo

[arekolek]

I have a question of my own regarding your code. Why don’t you write:

fun createView(context : Context) : View {
  return with(context) {
    frameLayout {
    }.also { view = it }
  }
}

Why assign to view twice?

[david.bilik]

Hi, because i have an error in code, the first assignment shouldnt be there because it wont compile

[arekolek]

I understand you can’t write view = frameLayout {}, but why assign twice? Why not assign only once in the also block like in the example I gave above?

[david.bilik]

As I said, i have an error in the code snippet, i forgot to delete the first assignment when i copy/pasted it. It should`ve been exactly like your code .)