all, I'm working through the kotlin koans, but the...

# getting-started

[jb]

all, I'm working through the kotlin koans, but the generics section trips me up a bit. I've been away from java for sometime, so humour me. In "fun <T, C:MutableCollection<T>> Collection<T>.partitionTo(first: C, second: C, predicate: (T) -> Boolean): Pair<C, C>", how should one read "<T, C: MutableCollection<T>>"? As I understand it, the code preceding the function name is the type parameter...but in this case, what is it stating the type is? The "," is throwing me for a loop...

[pavel]

T and C are both type parameters. Here we are extending MutableCollection of Ts with a method partitionTo that takes two Cs and a predicate from T to Boolean

[jb]

@pavel Thanks. Is there some docs which cover type parameters and their format/use? Should I understand it as "you can have any many type parameters as you want to use in your function, but just separate them with commas"? So I could have "fun <a,b,c,d,e,f> myFunc(..."

[pavel]

There might be a limit set by the compiler

[pavel]

regarding docs, I would start here: https://docs.oracle.com/javase/tutorial/java/generics/index.html

[pavel]

and then go here https://kotlinlang.org/docs/reference/generics.html

[jb]

@pavel Sure, but I'm understanding it correctly right? that the <> before the function name can accept 1..n type parameters (where n may be limited by the compiler)?

[pavel]

yes

[jb]

@pavel Ok, great. thanks. I think that clears it up. I have read that Kotlin page many times but it doesn't really go into type params that much. since I haven't been using java as much since generics came out, maybe the kotlin docs assume some knowledge of java generics syntax?

[pavel]

probably, when I played around with those I just assumed they worked the same as in Java and had no issues

[jb]

@pavel great...thanks very much for your help