Weekdays with iota

An enumeration in Go is a named integer type plus a block of constants. There is no enum keyword, and none is needed: iota and a defined type do the job.

iota is a counter that resets to 0 at the start of every const block and increases by one per line. Inside a block, a constant line with no expression repeats the previous one, so this declares three constants and not one:

type Level int

const (
	Debug Level = iota // 0
	Info               // 1
	Warn               // 2
)

Giving the type a String() string method makes it print as a name instead of a number, everywhere: fmt looks for that method on any value it formats.

Task

Finish main.go.

1. Replace the placeholder constants with one iota block declaring Sunday through Saturday as Weekday, numbered 0 to 6.
2. String() string returns the day's English name. A value outside 0..6 is not a day, and formats as Unknown(<n>): Weekday(9).String() is "Unknown(9)", and Weekday(-1) is "Unknown(-1)".
3. IsWeekend() bool is true for Saturday and Sunday only.
4. Next() Weekday returns the following day and wraps Saturday back to Sunday. A value outside 0..6 has no following day and comes back unchanged.

The tests check the numbers, the names, the wrap, and that fmt.Sprintf("%v", Friday) prints Friday rather than 5.

Hints

• Sunday Weekday = iota on the first line is what gives the whole block its type. The lines after it need no expression at all.

• A method is a function with a receiver in front of the name:

  func (d Weekday) IsWeekend() bool { ... }
  

  d is the value the method was called on, exactly like this elsewhere, and you pick its name. You will meet receivers properly in the methods concept; here you only need this one form.

• The names are easiest as a package-level array indexed by the day:

  var dayNames = [...]string{"Sunday", "Monday", ...}
  

  [...] sizes the array from the literal. Check the range before you index it: dayNames[9] panics, and the tests pass Weekday(9) on purpose.

• Write int(d) when formatting the unknown case. fmt.Sprintf("Unknown(%d)", d) would call String again and recurse until the stack runs out. That is the classic Stringer trap, and worth meeting once.

• d + 1 is a Weekday, not an int: arithmetic on a defined type stays in that type. That is exactly why the enum is a type of its own rather than a bare int.