adopting RandomAccessCollection protocol

(Don Giovanni) #1

I'm trying to adopt the RandomAccessCollection protocol from a class. I deliberately leave out the func index(before:) function because there is already a default implementation of that function in RandomAccessCollection. I do understand that that function's implementation is required because of BiDirectionalCollection from which RandomAccessCollection inherits.

My question is why would the compiler complain that func index(before:) implementation is required when there is already a default implementation in RandomAccessCollection that i can use?