Equatable with enum - Swift - swift

Question

How can I validate equal with below source code?
enum ErrorAPI: Equatable, Error {
case CannotFetch(String)
}
func ==(lhs: ErrorAPI, rhs: ErrorAPI) -> Bool {
switch (lhs, rhs) {
case (.CannotFetch(let a), .CannotFetch(let b)) where a == b:
return true
default:
return false
}
}

Answer 1

The enum case CannotFetch has an associated value of type String. That means, when the enum case is set to CannotFetch, a specific String is associated with that case. Read through the official Swift documentation about Enumerations if you need to understand Associated Values.
The func ==() method is a so called Equivalence Operator. You can read more about it in the official Swift documentation about Advanced Operators.
When comparing two enums, lets call them enumOne and enumTwo, this function is implemented to be able to compare those two enums if both cases are CannotFetch(String).
Example:
let enumOne = ErrorAPI.CannotFetch("Hi")
let enumTwo = ErrorAPI.CannotFetch("Hello")
if enumOne != enumTwo {
print("They are not equal!")
} else {
print("They are equal")
}
The line case (.CannotFetch(let a), .CannotFetch(let b)) where a == b: works as follows:
This case is only proceeded if both, enumOne and enumTwo, are set to the case CannotFetch(String)
Take the associated value (=String) of the left hand sided enum, i.e. "Hi" and assign it to the new constant let a.
Take the associated value (=String) of the left hand sided enum, i.e. "Hello" and assign it to the new constant let b.
Additionally, Check if the values behind the constants a and b are equal, i.e. Check if the Strings Hi and Hello are equal.
If all this is true, execute the code block in the case, i.e. return true