How to do if pattern matching with multiple cases?

Question

I'm searching for the syntax to do pattern matching with multiple cases in an if case statement. The example would be this:

enum Gender {
    case Male, Female, Transgender
}

let a = Gender.Male

Now I want to check, if a is .Male OR .Female. But I would like to avoid using switch for this. However the switch statement would be like this:

switch a {
case .Male, .Female:
    // do something
}

Is it possible to write this with if case? I would expect this, but it didn't work :(

if case .Male, .Female = a {

}

You should use a collection in js I would write something like this: `if ([Gender.Male, Gender.Female].includes(actualGender))`. — inf3rno, Sep 05 '16 at 16:18
To my knowledge, this is not possible. I created [a feature request](https://bugs.swift.org/browse/SR-4644) a while ago. — Raphael, Sep 19 '17 at 23:28

score 31 · Answer 1 · answered Sep 05 '16 at 17:41

31

A simple array does the trick:

if [.Male, .Female].contains(a) {
    print("Male or female")
} else {
    print("Transgender")
}

I'm simply amazed at Swift's ability to infer type. Here, it gets that .Male and .Female are of type gender from a.

answered Sep 05 '16 at 17:41

Code Different

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10

This only works if the enum is `Equatable`. An enum with an associated value for any case isn't, without manually implementing it. – rgeorge Jul 31 '17 at 18:47
1

@rgeorge You can always write a function if you need more than that. – inf3rno Sep 20 '17 at 18:02
3

@rgeorge True that the enum has to be `Equatable` - but, manual implementation is not necessary. Enums with associated values can automatically gain an implementation of `Equatable` if all of the associated value types are also `Equatable`. All you need to do is write the conformance in the declaration of the enum: `enum Gender: Equatable {`. *Note that the auto implementation is only gained if the conformance is declared in the initial declaration of the enum, not in an extension – jeremyabannister Oct 24 '18 at 17:08

score 2 · Answer 2 · edited May 23 '17 at 12:10

You should use a collection. In JavaScript I would write something like this:

if ([Gender.Male, Gender.Female].includes(actualGender))
    console.log(actualGender);

Note that I have not a clue about swift, or how to do the same in that language, so here is a relevant answer in the topic: https://stackoverflow.com/a/25391725/607033 :D

EDIT: This is the Swift version:

if [.Male, .Female].contains(a) {

}

score 2 · Answer 3 · answered Feb 10 '21 at 15:57

2

If you have an associated value, you can simply create a Bool variable like this

extension Gender {

var isMaleOrFemale: Bool {
    switch self {
    case .Male, .Female:
        return true
    default:
        return false
    }
}

And usage:

if a.isMaleOrFemale { 
// Your code here
}

answered Feb 10 '21 at 15:57

Alexander Nikolenko

485
6
10

This looks like correct solution because we avoid switch-case outside the enum. – Ilja Popov May 07 '21 at 19:55
This should be the accepted answer to this question – user3069232 Sep 14 '22 at 09:06

Zac Kwan · Answer 4 · 2016-09-05T16:10:38.240

0

For pattern matching, what you describe will not work yet. You could do this in your case. But if it cannot be convert into a hashValue. Then this would not work either.

// Using Pattern Matching for more than one case.
if case 0...2 = a.hashValue {
    print("Hello")
}

//Normal if else
if a == .Male || a == .Female {
    print("Hello")
}

edited Sep 05 '16 at 16:10

answered Sep 05 '16 at 15:48

Zac Kwan

5,587
4
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27

Yes, this would work, but is no pattern matching. Imagine there are more than two cases I want to check. Is there no syntax available for this purpose? – Ben Sep 05 '16 at 15:49
Aw, sorry i mis-read it. From what i know there is no pattern matching of what you describe. But there is a pattern that uses `hashValue` could work on your case. I will update my answer. – Zac Kwan Sep 05 '16 at 15:56
I don't see hashValue as an option in this case. Maybe I should better write a proposal if there is no syntax there yet :) – Ben Sep 05 '16 at 15:57
Ah ok, I see your point. This is not an option since the enum does not map to Int (and should not map to Int). – Ben Sep 05 '16 at 15:58
Currently, the only time i use a `if` for pattern matching, i only use it to map one case so i does not need to write a empty `default` in switch. Like `if case .Person(let age) = person where age <18` Other situation with more than one case that i need, i still use `switch`. – Zac Kwan Sep 05 '16 at 16:04
I see that using switch is much more powerful. But especially if I only want to check for one case and one case only I think it's just too much code to write with switch (and the default: break case..). – Ben Sep 05 '16 at 16:06
But certainly, it would be good if what you describe would work, but i don't think it will be in swift3 yet as there is no proposal for this. – Zac Kwan Sep 05 '16 at 16:06
That's what I should change I guess! :) – Ben Sep 05 '16 at 16:06
1

Note `==` will only work if the `enum` is `Equatable`, otherwise a `switch` statement as described in the original question is the correct approach. – Rich Sep 05 '16 at 19:44

How to do if pattern matching with multiple cases?

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