Enum Properties

Exercises

1. While we’ve defined the gets of our enum properties, we haven’t defined our sets. Redefine Validated’s valid and invalid properties to have a setter in addition to its getter.

   Solution

   We can redefine valid with the following setter.

   var valid: Valid? {
     get {
       guard
         case let .valid(value) = self
         else { return nil }
       return value
     }
     set {
       guard
         let newValue = newValue,
         case .valid = self
         else { return }
       self = .valid(newValue)
     }
   }
   

   While we must safely unwrap a non-optional newValue to reassign self, we also test that the current self is valid before doing so.

   The invalid property is the same boilerplate but uses the invalid case.

   var invalid: [Invalid]? {
     get {
       guard
         case let .invalid(value) = self
         else { return nil }
       return value
     }
     set {
       guard
         let newValue = newValue,
         case .invalid = self
         else { return }
       self = .invalid(newValue)
     }
   }
   

2. Take the valid setter for a spin. Assign Validated<Int, String>.valid(1) to a variable and increment the number using the setter.

   Solution

   There are a few ways of doing this! First, let’s assign a mutable variable.

   var v = Validated<Int, String>.valid(1)
   

   We can map over the optional Int returned by the valid getter.

   v.valid = v.valid.map { $0 + 1 }
   

   Or we can optionally chain with the += operator.

   v.valid? += 1