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?

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 }

.

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.

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

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.

I would use

also

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

+1 for

also

.

apply

sounds like do some stuff on foo, while

also

sounds like do something else with foo

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?

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

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?

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 .)