Swift : switch case multiples values from dictionary keys

Question

I would like to do a switch case for multiples values, where those values are get from keys of a dictionary.

myDict = ["dog": "waf", "cat": "meaow", "cow":"meuh"]
let animal = "cat"

switch animal {

case myDict.keys :
   print(myDict[animal])

case "lion" :
   print("too dangerous !")
}

default :
   print("unknown animal")
}

How can I get myDict keys and transform them to tuples (or something else)) ? I tried Array(myDict.keys) but it fails :

Expression pattern of type 'Array<String>' cannot match values of type
'String'

What do you want for tuple? Dict and Array gives almost everything you would need. — zc246, Feb 01 '16 at 13:55
switch statement does not on an Array, that's why I was trying to convert the dictionary keys to tuple. But I was in a wrong way, and Marc's solution is clearly the best. — Nahouto, Feb 01 '16 at 14:23
What you really want is to check key existence with `dict[key] != nil`. Don't think switch statement is suitable here. BTW, don't forget your `break` in switch statement. — zc246, Feb 01 '16 at 14:27
I can do like that : if key exist {do that} else {switch statement} but it is very long. Thanks for the break tip, it prevents the code to fall in two case statements — Nahouto, Feb 01 '16 at 14:34
@zcui93 In Swift, `switch` cases break by default. You have to use the `fallthrough` keyword to get the C behavior of falling through to the next case. — Marc Khadpe, Feb 01 '16 at 14:35

score 14 · Accepted Answer · answered Feb 01 '16 at 14:01

You can achieve what you want with a where clause. Here's how to do it.

let myDict = ["dog": "waf", "cat": "meaow", "cow":"meuh"]
let animal = "cat"

switch animal {

case _ where myDict[animal] != nil :
    print(myDict[animal])

case "lion" :
    print("too dangerous !")

default :
    print("unknown animal")
}

score -1 · Answer 2 · answered Jun 07 '23 at 16:26

Marc's answer is predicated on defining the key you're looking for first. If you want to iterate through all your keys, then run a for-loop over your dictionary using the tuples like you suggested:

let dictionary = ["Apple": 1, "Banana": 2, "Cherry": 3]

for (key, value) in dictionary {
    switch key {
    case "Apple":
        print("Apple's value is \(value)")
    case "Banana":
        print("Banana's value is \(value)")
    case "Cherry":
        print("Cherry's value is \(value)")
    default:
        print("Unrecognized key: \(key)")
    }
}

Note: The order of keys and values in a dictionary is not fixed, so the order of the print statements might be different each time you run the code.

Swift : switch case multiples values from dictionary keys

2 Answers2