swift case falling through

Question

Does swift have fall through statement? e.g if I do the following

var testVar = "hello"
var result = 0

switch(testVal)
{
case "one":
    result = 1
case "two":
    result = 1
default:
    result = 3
}

is it possible to have the same code executed for case "one" and case "two"?

score 387 · Accepted Answer · edited Nov 14 '17 at 11:17

387

Yes. You can do so as follows:

var testVal = "hello"
var result = 0

switch testVal {
case "one", "two":
    result = 1
default:
    result = 3
}

Alternatively, you can use the fallthrough keyword:

var testVal = "hello"
var result = 0

switch testVal {
case "one":
    fallthrough
case "two":
    result = 1
default:
    result = 3
}

edited Nov 14 '17 at 11:17

Twitter khuong291

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answered Jun 04 '14 at 23:05

Cezary Wojcik

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+1 for not just mentioning `fallthrough`, but suggesting to use multi-case – Thilo Jun 04 '14 at 23:07
3

This is such a good compromise between the danger of C's fall through, and the lack of fall through in for example, C# – Alexander Jun 11 '15 at 22:33
Does anyone know how to fall through from a case to default? case "two", default: won't compile. – Zack Morris Feb 05 '16 at 19:40
3

Never mind. I realized that commenting out the case makes it part of the default cases set, so: /*case "two",*/ default: has the effect I'm looking for. – Zack Morris Feb 05 '16 at 19:48
1

@AlexanderMomchliov C# has explicit fall through – Ian Newson Sep 16 '16 at 20:37
@IanNewson Oh i'm mistaken, I probably confused it for some other lang – Alexander Sep 17 '16 at 14:44
FWIW it's not good practice to only have a fallthrough in an otherwise empty case. – Aaron Nov 20 '18 at 22:57

score 8 · Answer 2 · edited Nov 13 '14 at 13:25

8

var testVar = "hello"

switch(testVar) {

case "hello":

    println("hello match number 1")

    fallthrough

case "two":

    println("two in not hello however the above fallthrough automatically always picks the     case following whether there is a match or not! To me this is wrong")

default:

    println("Default")
}

edited Nov 13 '14 at 13:25

Tieme

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answered Aug 03 '14 at 17:51

Glenn Tisman

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Do you know of a way to fall through to the default case? – MarcJames Jan 28 '16 at 16:08
7

i agree with "case two". For me this behavior sucks. Why does Swift execute the next case even it's not true? This makes the switch statement totally useless... – Andreas Utzinger Sep 22 '16 at 21:34

score 8 · Answer 3 · answered Nov 14 '17 at 11:28

Here is example for you easy to understand:

let value = 0

switch value
{
case 0:
    print(0) // print 0
    fallthrough
case 1:
    print(1) // print 1
case 2:
    print(2) // Doesn't print
default:
    print("default")
}

Conclusion: Use fallthrough to execute next case (only one) when the previous one that have fallthrough is match or not.

nhgrif · Answer 4 · 2017-02-19T14:20:07.133

7

case "one", "two":
    result = 1

There are no break statements, but cases are a lot more flexible.

Addendum: As Analog File points out, there actually are break statements in Swift. They're still available for use in loops, though unnecessary in switch statements, unless you need to fill an otherwise empty case, as empty cases are not allowed. For example: default: break.

edited Feb 19 '17 at 14:20

answered Jun 04 '14 at 23:05

nhgrif

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score 2 · Answer 5 · answered Jun 04 '14 at 23:05

2

The keyword fallthrough at the end of a case causes the fall-through behavior you're looking for, and multiple values can be checked in a single case.

answered Jun 04 '14 at 23:05

Russell Borogove

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swift case falling through

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