Swift integer type cast to enum

Question

I have an enum declaration.

enum OP_CODE {
    case addition
    case substraction
    case multiplication
    case division
}

And use it in a method:

func performOperation(operation: OP_CODE) {
        
}

We all know that how we can call this normally

self.performOperation(OP_CODE.addition)

But if I have to call it in some delegate where the integer value is not predictable, how do I call it?

For example:

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
     self.delegate.performOperation(indexPath.row)
}

Here, the compiler throws an error Int is not convertible to 'OP_CODE'. I've tried many permutations, but haven't been able to figure it out.

Gabriele Petronella · Accepted Answer · 2014-11-27 11:31:25Z

19

You need to specify the raw type of the enumeration

enum OP_CODE: Int {
    case addition, substraction, multiplication, division
}

addition will have a raw value of 0, substraction of 1, and so on.

and then you can do

if let code = OP_CODE(rawValue: indexPath.row) {
    self.delegate.performOperation(code)
} else {
   // invalid code
}

More info here: https://developer.apple.com/library/ios/documentation/swift/conceptual/Swift_Programming_Language/Enumerations.html#//apple_ref/doc/uid/TP40014097-CH12-XID_222

for older swift releases

In case you're using an older version of swift, raw enumerations work a bit different. In Xcode < 6.1, you have to use fromRaw() instead of a failable initializer:

let code = OP_CODE.fromRaw(indexPath.row)

edited Nov 27, 2014 at 11:31

answered Nov 27, 2014 at 10:50

Gabriele Petronella

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7 Comments

Mehul Patel Over a year ago

Tried it. Got an error OP_CODE cannot be constructed it has no accessible initializers- Can you please brief it.

Gabriele Petronella Over a year ago

I might have put a typo, try now

Gabriele Petronella Over a year ago

I tried the code and it works on my side, which version of Xcode are you on?

Mehul Patel Over a year ago

Xcode - Version 6.0.1 (6A317) & OS X Yosemite version 10.10

Gabriele Petronella Over a year ago

that's an old version, in that case you can use OP_CODE.fromRaw(indexPath.row), but you should really upgrade to 6.1

|

Antonio · Accepted Answer · 2014-11-27 11:19:41Z

You can use raw values in your enum:

enum OP_CODE : Int{
    case addition = 0
    case substraction = 1
    case multiplication = 2
    case division = 3
}

and use the failable initializer taking a raw value as input:

let code = OP_CODE(rawValue: 2) // code == .multiplication

Note that code is an optional, because if the raw value doesn't map to a valid enum, the initializer returns nil.

In your case:

func tableView(tableView: UITableView, didSelectRowAtIndexPath indexPath: NSIndexPath) {
    let code = OP_CODE(rawValue: indexPath.row)
    if let code = code {
        self.delegate.performOperation(code)
    }
}

Moreover, given an instance of the enum, you can obtain the associated raw value using the rawValue property.

Note: enums have changed a little bit in Xcode 6.1 - if you're using a previous version, read @GabrielePetronella's answer and related comments.

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