JuniorTheoryCommon

What happens when this program is compiled and run?

SWIFT

let numbers = [1, 2, 3]
numbers.append(4)
print(numbers)

It does not compile

Expecting [1, 2, 3, 4]: thinking let fixes only the name. In Swift an array declared with let is a constant as a whole, so append does not compile.
Expecting a crash on the append line: Swift checks changes to constants while compiling, before a single line runs.

What does the program print if numbers is declared with var?
Which of numbers + [4] and numbers.append(4) works with a let array, and why?

JuniorTheoryCommon

SWIFT

let numbers = [1, 2, 3]
numbers.append(4)
print(numbers)

It does not compile

Expecting [1, 2, 3, 4]: thinking let fixes only the name. In Swift an array declared with let is a constant as a whole, so append does not compile.
Expecting a crash on the append line: Swift checks changes to constants while compiling, before a single line runs.

What does the program print if numbers is declared with var?
Which of numbers + [4] and numbers.append(4) works with a let array, and why?