Trailing lambda and trailing comma are the 2 important Kotlin features that you must know if you're new to Kotlin!
Trailing lambda is something new in Kotlin that other programming language doesn't have. At least, I do not aware of any other programming language that supports it.
When you see code like this:
var result = operateOnNumbers(a, b) { input1, input2 ->
input1 + input2
}
println(result)
It means operateOnNumbers()
has 3 parameters. The last parameter is a function definition, which you usually either pass in the function reference or lambda.
var result = operateOnNumbers(
input1 = a,
input2 = b,
operation = { input1, input2 ->
input1 + input2
}
)
println(result)
Somehow I am still not getting used to this trailing lambda syntax. It looks like a function implementation.
So my mind always needs to automatically map to this (the code outside the parentheses is the last parameter of the function) every time I see the Trailing Lambda syntax.
The signature and implementation of operateOnNumbers()
looks like this:
fun operateOnNumbers(
input1: Int,
input2: Int,
operation: (Int, Int) -> Int): Int {
return operation(input1, input2)
}
On the other hand, trailing commas is pretty common in other languages.
With Trailing Comma
var result = operateOnNumbers(
a,
b, // trailing comma here
) { input1, input2 ->
input1 + input2
}
Without Trailing Comma
var result = operateOnNumbers(
a,
b // no trailing comma here
) { input1, input2 ->
input1 + input2
}
The benefit of using it is allowing easier diff and merge. For me, it makes my copy-and-paste life easier. Yupe, I do a lot of copy & paste!
Conclusion
I hope you enjoy this short post. I want to blog about this (especially Trailing Lambda) because it sometimes looks confusing to me. The function call is a bit complex. I always need to remind myself, the code outside the parentheses is the last parameter of the function.
Originally published at https://vtsen.hashnode.dev.
Top comments (2)
I think not having the trailing comma is more readable. My IDE highlights this as a problem.
useless trailing comma
Not that bad for me. Having said that, most of my code doesn't have the trailing comma. No complaints from my IDE.