A warning didn't appears after compiled, why it warns me?

Question

I create an enumeration contains all months of the year. The computed value of the enumeration returns the university semesters based on the input month

enum Month{
    case January, February, March, April, May, June, July, August, September, October, November, December


var schoolSemester: String {
            switch self {
        case .April, .September, .October, .November, .December:
            return "Autumn"
        case .January, .February, .March, .April, .May:
            return "Sping" // Here comes the warning
       default:
            return "Not in the school year"
        }
    }
}

var whichSemester = Month.February
print(whichSemester.schoolSemester)//even though the warning says this will never be executed, but it was executed!

Question1: Why Xcode keeps telling me that the second case will never be executed (which is wrong! I did execute the case by assign the February to the Month)

Question 2: Is calculated property a Lazy property?

Thanks a lot for your time and help

Answer 1

The compiler issues a warning because you apparently mistyped .August as .April in the first case, so that .April occurs in both cases.

The compiler could not notice that you omitted .August because you used a default case. It is therefore better to list all possible enumeration values explicitly instead:

var schoolSemester: String {
    switch self {
    case .April, .September, .October, .November, .December:
        return "Autumn"
    case .January, .February, .March, .April, .May:
        return "Spring"
    case .June, .July:
        return "Not in the school year"
    }

Now the compiler issues both a warning and an error

warning: case will never be executed
        case .January, .February, .March, .April, .May:
error: switch must be exhaustive, consider adding a default clause 

and the code does not compile. It forces you to check all cases again, and you'll quickly notice that .August is missing.