Hi What is this feature called in Kotlin, where we call a function with :: ? ``` ```fun someFunction...

# getting-started

[Danish Ansari]

Hi
What is this feature called in Kotlin, where we call a function with :: ?

```fun someFunction(param: (String) -> Unit) {}

class SomeClass {
    fun functionWithOneParameter(param: String) {}
}

// caller place
// what is this :: notation called?
val someClass = SomeClass()
someFunction(param = someClass::functionWithOneParameter)

[Paul Griffith]

probably ‘callable reference’
https://kotlinlang.org/docs/reflection.html#callable-references

[Danish Ansari]

Thank you

[Vampire]

And just to make it clear, you are not calling the function where you reference it with ::. 🙂

[Danish Ansari]

So we are just passing the reference and not actually calling it?

Now I wonder if there is any performance difference or some other difference when reference with :: and actually calling the function?

[Vampire]

It's not so much about performance, it is simply a different use-case.
You can for example give callbacks like that, that are then called on certain events and similar.

[Danish Ansari]

Got it, thanks

[Paul Griffith]

it can be thought of as syntactically cleaner, because you know for sure that you’re using another method verbatim instead of (possibly) hiding some side effect in a lambda
AFAIK the performance is basically equivalent on modern JVMs, or at least not something you should really care about 99% of the time

[ephemient]

the call performance is the same

[ephemient]

the construction performance (if it's not inlined) may be different as callable references have a few additional features that lambdas don't have

[Stephan Schröder]

"callable reference" 6 syllables 😬, that's probably why this is called a "tear-off" in other languages.