How to Increment a Swift Int Enumeration

how to increment a swift int enumeration

This is not C, where enums are integers. In swift an enum is a proper type in it's own right and you cannot perform math operations on it.

However, you can grab the raw value which is an integer, and do math on that. Then create a new enum:

var newState = MainState(rawValue: state.rawValue + 1)

Note that "newState" is an optional. You'll get null if rawValue + 1 doesn't exist in the enum.

Swift Increment through Enum

Update Starting with Swift 4.2 you can make use of the newly added support CaseIterable protocol, which adds compiler support for generating a list of all cases for an enum. Though @ninestones's comment pointed put that we are not guaranteed for allCases to return the cases in the same order as defined, the synthesized implementation does this, and it's unlikely that definition will change.

Your enum could then look something like this (no more hardcoded start value):

enum CopyState: CaseIterable {
    case binary, hex, both

    mutating func next() {
        let allCases = type(of: self).allCases
        self = allCases[(allCases.index(of: self)! + 1) % allCases.count]
    }
}

You can make this piece of functionality available to all CaseIterable enums:

extension CaseIterable where Self: Equatable {
    mutating func next() {
        let allCases = Self.allCases
        // just a sanity check, as the possibility of a enum case to not be
        // present in `allCases` is quite low
        guard let selfIndex = allCases.index(of: self) else { return }
        let nextIndex = Self.allCases.index(after: selfIndex)
        self = allCases[nextIndex == allCases.endIndex ? allCases.startIndex : nextIndex]
    }
}

enum CopyState: CaseIterable {
    case binary, hex, both
}

var state = CopyState.hex
state.next()
print(state) // both
state.next()
print(state) // binary

Or, a little bit more verbose, but with a better separation of concerns:

extension Collection {
    // adding support for computing indexes in a circular fashion
    func circularIndex(after i: Index) -> Index {
        let nextIndex = index(after: i)
        return nextIndex == endIndex ? startIndex : nextIndex
    }
}

extension Collection where Element: Equatable {
    // adding support for retrieving the next element in a circular fashion
    func circularElement(after element: Element) -> Element? {
        return index(of: element).map { self[circularIndex(after: $0)] }
    }
}

// Protocol to allow iterating in place (similar to a type conforming to both Sequence and IteratorProtocol)
protocol InPlaceIterable {
    mutating func next()
}

extension InPlaceIterable where Self: CaseIterable, Self: Equatable {
    // adding default implementation for enums
    mutating func next() {
        self = type(of: self).allCases.circularElement(after: self)!
    }
}

// now the enums need only the protocol conformances, they get the
// functionalities for free
enum CopyState: CaseIterable, InPlaceIterable {
    case binary, hex, both
}

---

You could use Int as raw value for your enum (note that this is also the default raw value if you don't specify it), and use it like this:

enum CopyState: Int {
    case binary, hex, both

    mutating func next(){
        self = CopyState(rawValue: rawValue + 1) ?? .binary
    }
}

var state = CopyState.hex
state.next()
print(state) // both
state.next()
print(state) // binary

This works fine as long as you have the raw values of the enum cases in consecutive order. By default the compiler assigns consecutive raw values.

You'd also need to keep in mind to update the next() method if the first case changes, otherwise it will no longer correctly work.

An alternative to the above limitation, suggested by @MartinR, is to force unwrap the raw value zero:

mutating func next(){
    self = CopyState(rawValue: rawValue + 1) ?? CopyState(rawValue: 0)!
}

The above code won't require updating the method when the first enum case changes, however it has the potential of crashing the app if the starting raw value of the enum changes.

How to get next case of enum(i.e. write a circulating method) in Swift 4.2

Some problems with your approach are:

• The Collection protocol does not define a last property.
• In order to compare the elements with == they have to be Equatable.
• Collection indices are not necessarily integers, they must be incremented
  with index(after:).

This seems to be a working solution (tested with Xcode 10.0 beta 2):

extension CaseIterable where Self: Equatable {
    func next() -> Self {
        let all = Self.allCases
        let idx = all.firstIndex(of: self)!
        let next = all.index(after: idx)
        return all[next == all.endIndex ? all.startIndex : next]
    }
}

Example:

enum Direction: CaseIterable {
    case east, south, west, north
}

print(Direction.east.next()) // south
print(Direction.north.next()) // east

Remarks:

• Only enumerations without associated values are CaseIterable, and
  those are also Equatable (but the compiler does not figure out that
  by itself). Therefore Self: Equatable is not a
  real restriction.
• Self.allCases can be used in Swift 4.2 to access the type property
  from an instance method.
• The forced unwrapping is safe because we know that the value is
  an element of allCases.
• Your enum Direction: CaseIterable compiles because the concrete
  enum Direction type is Equatable, and its Direction.allCases is an Array – which has integer indices and a last property.

Is there a pretty way to increment an optional Int?

For the sake of completeness, Optional has a map() method:

/// If `self == nil`, returns `nil`.  Otherwise, returns `f(self!)`.
@warn_unused_result
@rethrows public func map<U>(@noescape f: (Wrapped) throws -> U) rethrows -> U?

Therefore

index != nil ? index! + 1 : nil

is equivalent to

index.map { $0 + 1 }

How do I get the count of a Swift enum?

As of Swift 4.2 (Xcode 10) you can declare
conformance to the CaseIterable protocol, this works for all
enumerations without associated values:

enum Stuff: CaseIterable {
    case first
    case second
    case third
    case forth
}

The number of cases is now simply obtained with

print(Stuff.allCases.count) // 4

For more information, see

• SE-0194 Derived Collection of Enum Cases

+=' produces '()'. How can i return an incremented value from a closure

Just another way, use defer to increment counter after return

func countingClosure() -> (() -> Int) {
    var counter = 0
    let incrementCounter: () -> Int = {
        defer {
            counter += 1
        }
        return counter
    }
    return incrementCounter
}

How to write mutating function for enum in Swift

Using self = .apple(x) will do the trick. It is customary, but you already knew this.

enum Fruit {
    case apple(Int)
    case banana(Int, Int, Int)

    mutating func increment() {
        switch self {
        case let .apple(x):
            self = .apple(x + 1)
        case let .banana(x, y, z):
            self = .banana(x + 1, y + 1, z + 1)
        }
    }
}

var a = Fruit.banana(100, 200, 300)
a.increment()

---

You could also add support for generic operators:

enum Fruit {
    case apple(Int)
    case banana(Int, Int, Int)

    mutating func operate(_ op: (Int, Int) -> Int,_ num: Int) {
        switch self {
        case let .apple(x):
            self = .apple(op(x, num))
        case let .banana(x, y, z):
            self = .banana(op(x, num), op(y, num), op(z, num))
        }
    }
}

var a = Fruit.banana(100, 200, 300)
a.operate(+, 1) // adds all by 1
a.operate(*, 500) // multiplies all by 500

---

You could also add support for an array of generic operators:

enum Fruit {
    case apple(Int)
    case banana(Int, Int, Int)

    mutating func operate(_ nest: [((Int, Int) -> Int, Int)]) {
        for i in nest {
            switch self {
            case let .apple(x):
                self = .apple(i.0(x, i.1))
            case let .banana(x, y, z):
                self = .banana(i.0(x, i.1), i.0(y, i.1), i.0(z, i.1))
            }
        }
    }
}

var a = Fruit.banana(100, 200, 300)
a.operate([(+, 500), (*, 2)]) // Adds all by 500, then multiply all by 2

---

Here's a nice simplification

If it were up to me, this is what I would do to get rid of repeating self =. You can simplify this further if you wish.

enum FruitList: String { case apple, banana }
struct Fruit {
    static func apple(_ one: Int) -> Fruit {
        return Fruit.init(.apple, [one])
    }
    static func banana(_ one: Int,_ two: Int,_ three: Int) -> Fruit {
        return Fruit.init(.apple, [one, two, three])
    }
    
    var picked: (FruitList, [Int])
    init(_ fruit: FruitList,_ list: [Int]) {
        picked = (fruit, list)
    }
    
    mutating func operate(_ nest: [((Int, Int) -> Int, Int)]) {
        for i in nest {
            for j in 0..<picked.1.count {
                picked.1[j] = i.0(picked.1[j], i.1)
            }
        }
    }
}

var a = Fruit.apple(100)
a.operate([(+, 500), (*, 2)]) // Add all by 500, then multiply all by 2

fast enumeration for loop - Is there a counter?

You can't. Or better, you can use an external counter and manually increment it at every cycle, but then it would be easier to use "classical" for.

How do I increment a label value with a button press in Swift

You can fix this error by changing the offending code to the following:

cur = Int(money.text!)!;

Read more about initializers here. An excerpt:

Initialization is the process of preparing an instance of a class,
structure, or enumeration for use. This process involves setting an
initial value for each stored property on that instance and performing
any other setup or initialization that is required before the new
instance is ready for use.

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