don t people find it confusing that `Any toString ` returns

Question

don t people find it confusing that `Any toString ` returns null rather than actual null

Ruckus · Answer

Of course not `fun Any toString String` clearly returns `String` not `String `

Dias · Answer

it s only clear if you look at the definition of Any toString

ghedeon · Answer

It is confusing It s one of those behaviours that you have to remember Which usually means that you learn it by surprise I had to look it up in the source code first time I saw it

karelpeeters · Answer

That s true but you only need to look it up once simple smile

ghedeon · Answer

Personally I was expecting ` ` but I guess it s made like this in order to mark it as a special case idk

karelpeeters · Answer

Then tostring for data classes would suck `Point x=5 y= `

Ruckus · Answer

I disagree that it s one of those behaviors you have to remember If we re talking about `Any toString ` we re talking about the definition If we re talking about usage it s fairly clear if I say `value toString ` vs `value toString ` If you understand nullability and safe execution in Kotlin it seems perfectly clear

ghedeon · Answer

Nullability is unrelated in my answer mostly focused on the returned value Seeing null string as item somewhere in the final collection or even as a button label on the screen was surprising because it s not a specified constant in java Could be as well any kind of special string deliberately chosen by JB I m not saying it s wrong I m saying that a lot of people will fail to guess what `null toString ` is going to return from the first look

orangy · Answer

Guess the value of `String valueOf null ` expression in Java wink

ghedeon · Answer

I stand corrected then But I ve seen a few times people redefining this behaviour to ` ` mostly in UI layer because it makes more sense there Anyhow thankfully custom extensions are easy to write

cbruegg · Answer

But I don t like that functions may have nullable receivers As extension methods are supposed to mimic instance methods it s surprising this works

Burkhard · Answer

I guess allowing `null` as the receiver of extension functions is a different discussion and something that will probably never change Anyhow I like it Functions like `isNullOrEmpty` are great

Ruckus · Answer

gt As extension methods are supposed to mimic instance methods That seems a rather unfounded claim Can you justify it

cbruegg · Answer

Quite simply that at the callsite they are indistinguishable from them

Ruckus · Answer

There s a significant gap between sharing a common syntax and supposed to mimic

cbruegg · Answer

Fair point

cbruegg · Answer

Doesn t make my first time seeing this working less surprising though

Ruckus · Answer

I can see where you re coming from but the distinction between member and extension and their associated strengths and limitations isn t just important it s quite useful < elizarov> has a great overview of this in his Extension oriented design article

Burkhard · Answer

Also I don t think there is a good way of avoiding that Changing the calling syntax for extension functions would take away a lot of it s power and probably end up like c++ with ` ` vs ` gt `

Ruckus · Answer

< cbruegg> There were quite a few things with Kotlin I found surprising when I first saw them working but I never found that surprise detrimental To the contrary many of those surprises are precisely what make Kotlin such a pleasure to work with They re good surprises if you will slightly smiling face