If I have a protocol that has an optional property, and a class that needs to conform to the protocol which has the same property already, but as a non-optional property, how do I make the class conform to the protocol.
protocol MyProtocol {
var a: String? { get set }
}
class MyClass {
var a: String
}
extension MyClass: MyProtocol {
// What do I put here to make the class conform
}
Unfortunately, you can't redeclare the same variable in MyClass with a different type.
What Dennis suggests will work, but if you want to keep your variable in MyClass non-Optional, then you could use a computed property to wrap around your stored variable:
protocol MyProtocol {
var a: String? { get set }
}
class MyClass {
// Must use a different identifier than 'a'
// Otherwise, "Invalid redeclaration of 'a'" error
var b: String
}
extension MyClass: MyProtocol {
var a: String? {
get {
return b
}
set {
if let newValue = newValue {
b = newValue
}
}
}
}
a can either be a String or a String?, the compiler won't be able to infer the correct type of a whenever it is referenced. This breaks type-safety and makes it more difficult to reason about your code.
You just have to make the property of the class optional as well in order to conform to the protocol, as follows:
protocol MyProtocol {
var a: String? { get set }
}
class MyClass {
var a: String? // Added '?'
}
extension MyClass: MyProtocol {
// Nothing needed here to conform
}
a,MyClasssatisfies a stronger postcondition than the protocol requires. Except ifais required writable thenMyClassfails, since it also strengthens the precondition - the protocol requires the optionality. But if the protocol statedaasgetonly, then is it true that a non-optional implementation ofacould indeed conform? (Tested it doesn't)