I'm confused about when to use extension functions...

# getting-started

[thisen]

I'm confused about when to use extension functions. Take this example in Ktor: https://github.com/Kotlin/ktor/blob/master/ktor-core/src/org/jetbrains/ktor/http/ContentTypes.kt

It contains the ContentType class, but at line 120, this extension function is right next to the class:

fun ContentType.withCharset(charset: Charset) = withParameter("charset", charset.name())

Why isn't it placed inside the class?

[diesieben07]

thisen: In this case it looks like utility methods that are just simple helpers for other methods in the class are implemented as extension functions, which is the approach I would take, too. Then you don't have to clutter your class with those helper methods.

[thisen]

But the extension can be used "outside" this .kt file, right?

[diesieben07]

Yes, you just need to import it like a class.

[thisen]

Great. I get the idea. Thank you for the quick reply. 🙂