Strange behavior switch-case statement in Swift

Question

Usually the switch-case statement works like this: if the condition exactly matches the value, then the corresponding code block is executed. But in my case, something went wrong! Why does the code for "update" work for me while the condition is "date" !? I tried to recreate the situation in the playground - everything works correctly there. What is the problem?

Why does the update block work when key = "date"? Theoretically, the default block should work!?

My code:

print("Dictionary = \(dictionary)") for (key, value) in dictionary { switch key { case BaseDatabase.COLUMN_ID: // My code case WeddingDatabase.COLUMN_PREMIUM: // My code case BaseDatabase.COLUMN_UPDATE_CLEAN: print("type = \(BaseDatabase.COLUMN_UPDATE_CLEAN), key = \(key)") // My code default: // My default code } }

My console:

dictionary = ["note": <null>, "date": 2024-08-08 00:00:00, "update": 2019-07-09 08:57:05, "id_wedding": 1] type = update, key = date // WHY?? type = update, key = update

UPDATE:

Cut the code to the banal:

let key = "date" switch key { case "update": print("key = \(key)") break default: print("default = \(key)") break }

Added code in viewDidLoad empty viewController. The console still displays key = date. I see the problem ONLY in my project. I tried to add code in a new project and in playgroud - everything works fine (default = date is output to the console). How can this be? I tried different Simulators (and iOS versions) - the problem is still there. I also tried to clean the project - the problem persists. Maybe somewhere in the project the work of switch statement is redefined - is this possible?

@martin-r The problem is that in the standalone example, I do not observe such a problem. Everything works correctly. — Vergiliy
– Vergiliy, Commented Jul 9, 2019 at 13:00
How you defined BaseDatabase.COLUMN_ID, WeddingDatabase.COLUMN_PREMIUM and BaseDatabase.COLUMN_UPDATE_CLEAN ? — TheTiger
– TheTiger, Commented Jul 9, 2019 at 13:17
@TheTiger In the following way: static let COLUMN_ID = "_id", static let COLUMN_PREMIUM = "premium" and private static let COLUMN_UPDATE_CLEAN = "update" — Vergiliy
– Vergiliy, Commented Jul 9, 2019 at 13:25
A couple of things: First, your update 2 includes non-standard syntax (presumably reliant on other extensions you have in your project). I’d suggest you always keep your examples as simple as possible. E.g. static func ~= (lhs: String, rhs: String) -> Bool { return lhs.contains(rhs) } manifests the problem, too. Second, you should not put answers in your question, but rather post your own answer to your question. I think this a real gem you’ve found, but you’re making it hard for someone to vote for your question, much less your answer. — Rob
– Rob, Commented Jul 9, 2019 at 16:03

Vergiliy · Accepted Answer · 2019-07-10 06:04:52Z

I found a problem. In the String class extension, the ~= operator was redefined as follows:

extension String { static func ~= (lhs: String, rhs: String) -> Bool { return NSRegularExpression(rhs).matches(lhs) } }

As it turned out, the ~= operator is used in a switch statement. To correct the error, I replaced this extension with the following:

extension String { func matches(pattern: String) -> Bool { return NSRegularExpression(pattern).matches(self) } }

How I use it:

if value.matches(pattern: "#[0-9]{1,2}[A-Z]#" { // Code }

It should be very attentive when redefining operators!

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