I have a a Polygon class. I'm adding several opera...

# announcements

[hudsonb]

I have a a Polygon class. I'm adding several operators and useful functions. Would you add these as methods in the class, or as extension functions? Not concerned with Java interop.

[kevinmost]

I make it an extension if it's a pure function. It makes it clearer to the reader that those functions don't modify internal state.

[hudsonb]

Ah yes I should mention, it's immutable.

[kevinmost]

yeah, I personally think I'd rather see

data class Polygon(...)

operator fun Polygon.plus(other: Polygon): Polygon = ...

than

data class Polygon(...) {
  operator fun plus(other: Polygon): Polygon = ...
}

[kevinmost]

and I feel like I see extensions preferred over members throughout the stdlib

[serebit]

I make functions that don’t require access to private members into extensions

[hudsonb]

Thanks "rules of thumb" like this is what I was looking for

[serebit]

There’s nothing specific in the coding conventions, so ultimately it comes down to personal preference. That’s just our respective philosophies :)

[Dico]

I prefer members because I dislike having to import extension functions. It leads to too many * imports. Imports can play a role for code readability, especially for other developers. Repositories where I can deduce the location of a symbol's declaration from imports at the top are helpful.

[Dico]

I would probably adopt extension functions more if importing the type they extend, imports all of them in that file.

[gaetan]

I think that using extension functions is a clean way of putting the code at the right place.
In the case of Polygon + Polygon, it makes sense to keep this function as a member function.
I would use an operator extension function in the case of a bounded context.