As a relative new kotliner I still find when to use Extension functions vs methods not easy. I mean they both work right and obvious cases with third party libs are easy. Is there any glaring down sides to extensoin functions other than tighter coupling? I have to import the functions at call site which I don't when using a method? I get there might be a tiny performance boost from the static dispatch but surely the compiler could do the same dispatch in many cases for methods as well?

Downsides to extension functions: they cannot be inherited/overriden by children classes, so it's not possible for a child to provide a faster implementation

Thx I will read it asap!

In case you didn't notice, the author is Roman Elizarov, the Project Lead for Kotlin. There's essentially no answer that's more authoritative than this 🙂 I highly recommend his blog posts in general, they're all very well written.

I did notice 🙂 I got the idea but I would like even more description of the do's-and-dont's. I mean you learn as you make mistakes but it's always faster to learn from someone else's experience