Swift Switch Case Compiler Error

Swift switch statement considered all cases of Int, but compiler still display error

Update for Swift 3: Swift 3 introduced ClosedRange which makes
it possible to define a range like 1...Int.max including the
largest possible integer (compare Ranges in Swift 3). So this compiles and works as expected,
but still requires a default case to satisfy the compiler:

extension Int {
    enum Kind {
        case negative, zero, positive
    }
    var kind: Kind {
        switch self {
        case 0:
            return .zero
        case 1...Int.max:
            return .positive
        case Int.min...(-1):
            return .negative
        default:
            fatalError("Oops, this should not happen")
        }
    }
}

There are other bug reports where the Swift compiler does not
correctly determine the exhaustiveness of switch-statements, such
as https://bugs.swift.org/browse/SR-766, where Apple engineer Joe Groff
commented:

Unfortunately, integer operations like '...' and '<' are just plain functions to Swift, so it'd be difficult to do this kind of analysis. Even with special case understanding of integer intervals, I think there are still cases in the full generality of pattern matching for which exhaustiveness matching would be undecidable. We may eventually be able to handle some cases, but there will always be special cases involved in doing so.

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Old answer: The compiler is not so smart to recognize that you have covered
all possible cases. One possible solution is to add a default
case with a fatalError():

var kind: Kind {
    switch self {
    case 0:
        return .Zero
    case let x where x > 0:
        return .Positive
    case let x where x < 0:
        return .Negative
    default:
        fatalError("Oops, this should not happen")
    }
}

Or make case 0: the default case:

var kind: Kind {
    switch self {
    case let x where x > 0:
        return .Positive
    case let x where x < 0:
        return .Negative
    default:
        return .Zero
    }
}

(Remark: I initially thought that the following would work correctly
without needed a default case:

var kind: Kind {
    switch self {
    case 0:
        return .Zero
    case 1 ... Int.max:
        return .Positive
    case Int.min ... -1:
        return .Negative
    }
}

However, this compiles, but aborts at runtime because you cannot
create the range 1 ... Int.max. More information around this
problem can be found in the article Ranges and Intervals in Swift.)

Swift compiler crashes on switch statement, need workaround

Credit to the solution really goes to everyone who commented above.

The problem seems to be that the Swift compiler wants to know exactly how large the enum is in memory. Generics make that impossible, thus the compiler does not behave correctly.

The solution I went with was taken from Rob Rix's library, which is to box the generic in another type. Note that it must be a class, since a reference has a known size but a struct with the generic does not.

The @autoclosure solution seemed interesting also, but it does not work with the latest version of Xcode. This was by design; as I understand, the developers don't want closures to run each time the enum is evaluated.

Thanks everyone!

Expected declaration on switch declaration

You can't write switch rank { inside the struct directly , it should be inside a function init or any other custom one

public struct beltRank {
  var rank = 0
  var belt = ""
  init(rank:Int) {
    // write switch here
  }
}

Switch Statement Must Be Exhaustive - Xcode bug?

If you write it like this, you won't get an error (Xcode 9 beta 2):

import Foundation

enum Search {
    case sets(query: String?, creator: String?, imagesOnly: Bool?, autocomplete: Bool?, modifiedSince: TimeInterval?, page: Int?, perPage: Int?)
    case classes(query: String, page: Int?, perPage: Int?)
    case universal(query: String, page: Int?, perPage: Int?)

    public var baseURL: String { return "" }
    public var version: Float { return 0 }

    public var path: String {
        switch self { // Switch must be exhaustive ERROR.
        case .sets(_, _, _, _, _, _, _):
            return "search/sets"
        case .classes(_, _, _):
            return "search/classes"
        case .universal(_, _, _):
            return "search/universal"
        }
    }
}

If I'm going to be doing much matching, I usually prefer to wrap the associated values in separate structs. This makes for simpler patterns and for less work when changing the nature of the associated values. Thus:

enum Search {

    struct Sets {
        var query: String?
        var creator: String?
        var imagesOnly: Bool?
        var autocomplete: Bool?
        var modifiedSince: TimeInterval?
        var page: Int?
        var perPage: Int?
    }

    case sets(Sets)

    struct Classes {
        var query: String
        var page: Int?
        var perPage: Int?
    }

    case classes(Classes)

    struct Universal {
        var query: String
        var page: Int?
        var perPage: Int?
    }

    case universal(Universal)

    public var baseURL: String { return "" }
    public var version: Float { return 0 }

    public var path: String {
        switch self { // Switch must be exhaustive ERROR.
        case .sets(_):
            return "search/sets"
        case .classes(_):
            return "search/classes"
        case .universal(_):
            return "search/universal"
        }
    }
}

Swift switch default + fallthrough: missing return in a function expected to return 'String'

It's not clear whether you have figured this out or not. The problem is not that you haven't got all bases covered in your switch statement. It is that not all code paths return a value. In the ApiError case, if the test fails, there is no return executed. If you put a return after this test, the code will compile.

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