JuniorTheoryCommon

What does the program print?

SWIFT

struct Day: CustomStringConvertible {
    var n: Int
    var description: String { "day \(n)" }
}
var today = Day(n: 3)
today.n += 1
print(today)

day 4

Expecting Day(n: 4): thinking print ignores description. Once the type declares CustomStringConvertible, print shows the text description returns.
Expecting day 3: treating description as text saved at creation. It is computed on every read, so it shows n after n += 1.

What would the program print without : CustomStringConvertible in the declaration of Day?
What does string interpolation print when today is placed inside a string?

JuniorTheoryCommon

SWIFT

struct Day: CustomStringConvertible {
    var n: Int
    var description: String { "day \(n)" }
}
var today = Day(n: 3)
today.n += 1
print(today)

day 4

Expecting Day(n: 4): thinking print ignores description. Once the type declares CustomStringConvertible, print shows the text description returns.
Expecting day 3: treating description as text saved at creation. It is computed on every read, so it shows n after n += 1.

What would the program print without : CustomStringConvertible in the declaration of Day?
What does string interpolation print when today is placed inside a string?