EventCallback lt Float gt if it gt 0 println ouch else print

Question

EventCallback lt Float gt if it gt 0 println ouch else println 1 I don t understand the syntax put a type before a lambda is

Shawn · Answer

How familiar are you with generics

Shawn · Answer

you re not putting a type before a lambda you re passing in a type parameter to a genericized function

Ifvwm · Answer

I know generics but I don t know how generics work with lambda

Shawn · Answer

have you looked at this particular function definition

Shawn · Answer

if I had to guess it probably looks something like this ``` fun lt T gt EventCallback lt T gt block T gt Unit ```

Ifvwm · Answer

object EventCallback lt Float gt override fun onEvent arg0 Float Unit = if arg0 gt 0 println ouch else println 1

Shawn · Answer

that looks more accurate actually `EventCallback lt T gt ` would be an interface

Shawn · Answer

in this case a SAM interface

Shawn · Answer

you also want to use triple backticks ` ``` ` to wrap code and shift enter to insert newlines without sending messages

Ifvwm · Answer

``` object EventCallback lt Float gt override fun onEvent arg0 Float Unit = if arg0 gt 0 println ouch else println 1 ```

Ifvwm · Answer

I don t know this stuff turn to ``` EventCallback lt Float gt if it gt 0 println ouch else println 1 ```

Shawn · Answer

so if you ctrl cmd+b into EventCallback you ll see the definition of the interface

Shawn · Answer

probably looks like this if I had to guess

Shawn · Answer

``` public interface EventCallback lt T gt void onEvent T arg0 ```

Shawn · Answer

with a single method defined making it a Single Abstract Method interface which can be converted to a lambda

Ifvwm · Answer

aha

Shawn · Answer

Kotlin lets you implement SAMs with a single lambda because it can substitute in for that single method

Shawn · Answer

you need to provide a parameter for `T` if it can t be inferred

Ifvwm · Answer

ok

Shawn · Answer

you could probably do something like this if you wanted ``` EventCallback param Float gt if param gt 0 println ouch else println 1 ```

Ifvwm · Answer

what this `it here means

Ifvwm · Answer

should it be param

Shawn · Answer

Shawn · Answer

you really should read through the docs if you haven t already

Ifvwm · Answer

fine

Ifvwm · Answer

but your code is ```

Ifvwm · Answer

``` param Float gt if it gt 0 ```

Shawn · Answer

That might not work actually depends on if type inference is smart enough in this case

Ifvwm · Answer

I thought it should be ``` it Float gt if it gt 0 ```

Shawn · Answer

you can explicitly type `it` or you can pass an explicit parameter to the interface

Shawn · Answer

ah I see

Shawn · Answer

I typo d my bad

Ifvwm · Answer

this lambda stuff in kotlin seems wonderful

Shawn · Answer

They re pretty great I d consider their use to be a defining feature of the language

Ifvwm · Answer

aha That s because Kotlin has SAM single abstract method only for Java interfaces