Is possible to compare Enum values with 'if' statement?

Question

I create a enum type (Swift 4.0):

enum TraceResult{
    case nothing
    case success
    case failed
    case custom(String)   //#1
}

after that I decide to compare two enum values :

let tr = TraceResult.nothing
if tr == TraceResult.success{    //#2
    //do something...
}

and compiler will complain a error in line #2:

Binary operator '==' cannot be applied to two 'TraceResult' operands

If I remove line #1,It's all right!!!

Or I used 'switch' statement to compare them ,It's also OK!!!

So Is possible to compare two TraceResult values with 'if' statement???

Thanks ;)

if I feel below 2 answers is all right,what should I do???How to select the "right answer"??? Thanks! — hopy
– hopy, Commented Jun 15, 2018 at 2:43

Papershine · Accepted Answer · 2018-06-15 02:07:04Z

4

if case can be used to compare enum values.

You use

if case .success = tr {
    // do something
}

Instead of the == comparison you are doing currently.

answered Jun 15, 2018 at 2:07

Papershine

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1 Comment

Mamad Farrahi Over a year ago

@hopy please mark this answer as correct cause it's the easier way.

Alexander · Accepted Answer · 2018-06-15 02:01:45Z

You need to declare a conformance to Equatable for your type:

enum TraceResult: Equatable {
    case nothing
    case success
    case failed
    case custom(String)
}

As of Swift 4.1, the compiler will automatically synthesize the definition of the == function for you. Prior to 4.1, you would need to manually implement, like so:

extension TraceResult: Equatable {
    static func == (lhs: TraceResult, rhs: TraceResult) -> Bool {
        switch (lhs, rhs) {
            case (.nothing, .nothing): return true
            case (.success, .success): return true
            case (.failed, .failed): return true
            case (.custom(let s1), .custom(let s2)) where s1 == s2: return true

            case _: return false
        }
    }
}

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