is there any benefit in declaring the types of the...

# announcements

[Florian]

is there any benefit in declaring the types of the lambda parameters?

[alex]

better readability without IDE

[Irving Rivas]

also type safety, I guess? remember the last expression is sent back, it can be accidentally altered

(edit edit: I goofed a bit and edited in a hurry and was dumb. A better answer is: “`result` has an implicit type, derived of the types of acc and i. acc ’s type is determined from the 0 passed to fold as the first parameter and is considered to be the expected return type of the lambda. but i comes from the list, which could have other types, like Long or Double or String, thus altering result ’s type — adding an Int and a Long yields a Long, for instance. If you have the type in the arguments, it gets caught at the exact place of the issue (argument is not of the expected type), otherwise you get a return type mismatch.“)

[Florian]

thank you

[Florian]

although I don't get the last part

[Florian]

what type safety does this give me?

[Irving Rivas]

Bear with me, I’ll whip up a little example 🙂

[Florian]

thank you

[Irving Rivas]

so — OK imagine you have that very same lambda

[Irving Rivas]

imagine you didn’t specify the 2nd param is an Int

[Irving Rivas]

you could pass in eg a double

[Irving Rivas]

@Florian do you see what would happen?

[Florian]

but the type of the parameter isnt declared at this place right

[Florian]

this is the actual argument

[Irving Rivas]

Correct, it’s part of the function signature

[Irving Rivas]

In your example, if the list has val items = listOf(1, 2L, 3, 4L, 5), for instance, the lambda will throw.

[Florian]

maybe its too late for me to understand it

[Florian]

I have to try again tomorrow

[Irving Rivas]

maybe I’m awful explaining 🙂

[Florian]

but anyway, thank you for your help

[ephemient]

the compiler might not be able to deduce the right type without help, for example

items.fold(null) { acc, i -> ... }

isn't possible, the type has to be given with one of

items.fold<Int, String?>(null) { acc, i -> ... }
items.fold(null as String?) { acc, i -> ... }
items.fold(null) { acc: String?, i -> ... }

and out of these options, I'd prefer the last one