What does first parameter ` lt X gt ` stand for It always confused me

What I was looking for is generic functions but I don t get the point of it is this ```fun lt T gt singletonList item T List lt T gt ``` same as this ```fun singletonList item T List lt T gt ```

What does first parameter ` lt X gt ` stand for It always co kotlinlang #announcements

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Davor Maric

05/15/2018, 12:24 PM

What does first parameter

<X>

stand for? It always confused me..

Andreas Sinz

05/15/2018, 1:01 PM

is a generic type https://kotlinlang.org/docs/reference/generics.html

Davor Maric

05/15/2018, 1:24 PM

What I was looking for is generic functions.. but I don't get the point of it.. is this

fun <T> singletonList(item: T): List<T> { // ... }

same as this

fun singletonList(item: T): List<T> { // ... }

what the removed param stands for? It isn't return type as return type is specified after (args):

araqnid

05/15/2018, 2:28 PM

it specifies that the function call needs to have a T parameter inferred from the context it was called from

If you leave the <T> out in the lines above, then it will simply say it's unknown -- by putting it there you're "declaring" it local to the function declaration

(as opposed to inheriting it from the class the function is a member of or whatever)

specifically in this case, you're specifiying a constraint: the same type you pass as an argument is to be used for the return type

Davor Maric

05/15/2018, 2:47 PM

I am coming from Java World.. does this stuff exist in Java?

araqnid

05/15/2018, 3:29 PM

yes, Collections.singletonList() has a type parameter there too

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