JuniorTheoryCommon

What does the program print?

SWIFT

let csv = "red,,blue"
let parts = csv.split(separator: ",")
print(parts.count, parts.joined(separator: "-"))

2 red-blue

Expecting 3 red--blue: thinking split keeps an empty piece between two separators. Swift's split drops empty pieces by default, so red,,blue gives two parts.
Expecting 2 red-blue-: thinking joined adds the separator after every part. It puts the separator only between parts, so nothing follows the last one.

JuniorTheoryCommon

SWIFT

let csv = "red,,blue"
let parts = csv.split(separator: ",")
print(parts.count, parts.joined(separator: "-"))

2 red-blue

Expecting 3 red--blue: thinking split keeps an empty piece between two separators. Swift's split drops empty pieces by default, so red,,blue gives two parts.
Expecting 2 red-blue-: thinking joined adds the separator after every part. It puts the separator only between parts, so nothing follows the last one.