Example 1
enum Enum1: Int {
case ONE = 1
case TWO = 2
}
let a1 = Enum1.ONE
let b1 = Enum1.TWO
if a1 == b1 {
println("Equal")
} else {
println("Not equal")
}
Example 2
enum Enum2 {
case ONE
case TWO
}
let a2 = Enum2.ONE
let b2 = Enum2.TWO
if a2 == b2 {
println("Equal")
} else {
println("Not equal")
}
But if the enum has an associated value things get more difficult:
Example 3
enum Enum3 {
case ONE
case TWO(String)
}
let a3 = Enum3.ONE
let b3 = Enum3.TWO("wow")
if a3 == b3 {
println("Equal")
} else {
println("Not equal")
}
Will cause the following error: Binary operator '==' cannot be applied to two Enum3 operands
So how can we compare enums with an associated value?
The following pattern does that. I am not claiming that it is the only way, but so far its the best I can come up with. If you have something better, please let us know.
If we add the following function to the Enum3 example, everything compiles fine:
(Thanks to ibex10 for pointing out an error in the original pattern, this has now been fixed)
func == (left: Enum3, right: Enum3) -> Bool {
switch left {
case .ONE:
switch right {
case .ONE: return true
default: return false
}
case let .TWO(str1):
switch right {
case let .TWO(str2) : return (str1 == str2)
default: return false // Cover all cases
}
}
}
Happy coding...
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Good try but what happens with the following case?
ReplyDeletelet u = Enum3.ONE
let v = Enum3.ONE
if u == v {
print("Equal")
} else {
print("Not equal")
}
Infinite recursion.
Good catch!
DeleteYes, we need to use switch within switch for all cases.
I have updated the pattern so that this is now part of the post.
Thank you very much!
Here's a more compact way to define == for enumerations with associated values:
ReplyDeletefunc == (left: Enum3, right: Enum3) -> Bool {
switch (left, right) {
case (.ONE, .ONE):
return true
case (.TWO(let str1), .TWO(let str2)):
return str1 == str2
default:
return false
}
}
Very nice!, love it!
Deletevery thankful bro...
ReplyDelete