JuniorTheoryCommon

What does the program print?

SWIFT

let numbers = [1, 2, 3]
let result = numbers.filter { $0 < 3 }.map { $0 * 10 }
print(result)

[10, 20]

Expecting [30]: thinking filter removes the elements for which the closure returns true. It keeps them, so 1 and 2 stay and are multiplied.
Expecting [10, 20, 30]: thinking each call in the chain works on numbers. map gets the result of filter, [1, 2], so only two numbers are multiplied.

JuniorTheoryCommon

SWIFT

let numbers = [1, 2, 3]
let result = numbers.filter { $0 < 3 }.map { $0 * 10 }
print(result)

[10, 20]

Expecting [30]: thinking filter removes the elements for which the closure returns true. It keeps them, so 1 and 2 stay and are multiplied.
Expecting [10, 20, 30]: thinking each call in the chain works on numbers. map gets the result of filter, [1, 2], so only two numbers are multiplied.