Just because someone wandered along today asking about input from stdin. No guarantees about edge conditions.

import Foundation
import Darwin

var myString : UnsafeMutablePointer<Int8> = UnsafeMutablePointer.alloc(100)
println("Enter your name")
fgets(myString, 100, stdin)
let myName = String.fromCString(myString)
println("Hi \(myName!)")

With Swift, there’s almost always a better way to do things and when you get to that better way, it just rings with “of course”-ness.

As usual, this started as a question from a participant in #swift-dev. “This doesn’t work,” he said, and pasted the following.

func continueGame() {
    if self.gameLogic.count == 0 {
        return
    }
    self.gameLogic[0]()
    self.gameLogic.removeAtIndex(0)
}

So I started kicking the wheels on it. To get going, I decided to use the following array of closures to test my approaches.

[Void -> Void] = [{println("one")}, {println("two")}, {println("three")}]

First, I explained about using a generator and the next() function:

var myarray : [Void -> Void] = [{println("one")}, {println("two")}, {println("three")}]
var mygenerator = myarray.generate()

if let closure = mygenerator.next() {
closure()
}

if let closure = mygenerator.next() {
closure()
}

if let closure = mygenerator.next() {
closure()
}

That wasn’t practical for a generalized implementation.So I built a few loops that eventually ended up like this:

while true {
    if let closure = mygenerator.next() {
        closure()
    } else {
        break
    }
}

But Ken Ferry took one look at that, laughed, and suggested the following (far more elegant) solution instead:

while let closure = mygenerator.next() {closure()}

Beautiful and simple. Thanks, Ken.

Yesterday in #swift-lang, an enumeration discussion buzzed. A chat participant asked, “Is there any way to go backwards in an enum? I want to look up an enum based on a value.” The answer is simple and accessible. Creating enumerations from values returned by services and function represents an important touchpoint in Swift development.

RawRepresentable

The RawRepresentable protocol consists of two underlying functions: toRaw() and fromRaw(). These enable you to transform enumerations to and from underlying data states.

protocol RawRepresentable {
    typealias Raw
    class func fromRaw(raw: Raw) -> Self?
    func toRaw() -> Raw
}

For example, if you base your enumeration on integers, you can use the underlying sequence to move to and from that representation.

enum Nums : Int { 
    case Zero
    case One
    case Two
    case Three
}

var z : Nums = Nums.fromRaw(2)!
z == .Two // true
z == .Three // false

This example uses an Int raw-value type for its underlying representation. The type appears just after the name of the enumeration.

Fun with Raw Values

The enumeration values do not have to exactly match 0, 1, 2, etc. For example, you might assign arbitrary values to the enumeration entries.

enum Nums : Int {
    case Zero = 5
    case One = 30
    case Two = 15
    case Three = 20
}

var z : Nums = Nums.fromRaw(20)!
z == .Two // false
z == .Three // true
println(Nums.Three.toRaw()) // prints 20

Nor are your raw-convertible enumerations limited to integers. You have access to any equatable literal, specifically integer literals, floating-point literals, string literals, booleans, and nil. For example, you might use strings as raw values:

enum Lets : String {
    case X = "x"
    case Y = "y"
    case Z = "z"
}

var zz = Lets.fromRaw("z")
zz! == .Z // true
println(Lets.Y.toRaw())

Each case must declare a unique name and value. If you skip the value for integers, as in the first example in this post, they implicitly inherit their order. The count starts at zero and increases monotonically from there.

Raw vs Associated Values

Don’t confuse raw values with associated values. A raw value is constant across all uses of an enumeration. They are defined in the enumeration declaration at compile time. Associated values enable you to store typed information in an enumeration. These are defined at runtime.

enum CocoaResult {
    case success(NSObject) // associated success value
    case failure(NSError) // associated error value
}

Consider the following code snippet. It creates a closure that prints out the value of the variable i. When it runs, should it print out 25, the value of the variable at the time the closure was created, or 35, the current contents of the memory pointed to by the variable reference?

var i = 25
var cl = {println(i)}
i = 35
cl()

If you paste this snippet into a playground, you’ll find that this code prints 35, and not 25. That’s because Swift closures default to capturing references, not values. To change this behavior and capture the value, use a capture list, as in the following example.

var i = 25
var cl = {[i] in println(i)}
i = 35
cl()

The use of [i] enables you to capture the value of i at the time you create the closure instead of at a later runtime.

Capture lists appear as the first item in a closure. They’re listed before any parameter clauses or identifier lists and require the in keyword to be used. For example, here’s another closure. This one is String -> Bool. It more or less does the same work as the previous closure but offers extra syntactic elements so you can see a capture list in a more complex setting.

var anotherClosure = {
    [i] (x : String) -> Bool in
    println(i)
    return true
}

Here’s another example, one that uses a class instance instead of an integer.

class MyClass {
var value = "InitialValue"
}

var instance = MyClass() // original assignment
var cl2 = {[instance] in println(instance.value)}
instance = MyClass() // updated assignment
instance.value = "UpdatedValue"
cl2()

If you omit the [instance] in capture list, this example prints out “UpdatedValue”, the value associated with the updated variable assignment. With the capture list, it prints “InitialValue”. This is the value stored by the original assignment.

When working with classes, a capture list can add modifiers to captured elements, specifically weak, unowned, unowned(safe) and unowned(unsafe). According to the reference material I’ve been reading, you most commonly see modifier usage when you want to capture self without reference cycles. The Swift Programming Language offers the following example. Here, the capture list enables you to capture the reference to self as an unowned — instead of strong — reference, avoiding reference cycles.

lazy var asHTML: () -> String = {
        [unowned self] in
        if let text = self.text {
            return "<\(self.name)>\(text)"
        } else {
            return "<\(self.name) />"
        }
    }

Thanks Lily B.

It’s a lot easier than the docs make it out to be, especially if you’re just using a single target. Here’s my Swift file. Make sure you use the @objc keyword to tag your Swift classes so they’re available to your ObjC ones.

import Foundation

@objc class TestClass {
    class func `new`() -> TestClass {
        return TestClass()
    }
    
    func testFunction() {
        println("This function works")
    }
}

And here’s the Objective-C client:

#import "AppDelegate.h"
#import "TestProject-Swift.h"
@implementation AppDelegate
- (BOOL)application:(UIApplication *)application 
    didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    TestClass *instance = [TestClass new];
    [instance testFunction];
    return YES;
}
@end

The secret here is to import the name of the target in this case “TestProject” with the “-Swift.h” extension. Xcode builds this for you and hides it behind the scenes in the derived data. For the above example, mine was left at: DerivedData/TestProject-aqpeqeuqusyzdtcqddjdixoppyqn/Build/Intermediates/TestProject.build/Debug-iphoneos/TestProject.build/DerivedSources/TestProject-Swift.h

The .h file is actually quite interesting. Here is the interface that was built from my Swift code:

SWIFT_CLASS("_TtC11TestProject9TestClass")
@interface TestClass
+ (TestClass *)new;
- (void)testFunction;
- (instancetype)init OBJC_DESIGNATED_INITIALIZER;
@end

There’s also a bit of fascinating cookiecutter set-up to be found in the header file. I encourage you to take a peek.

Consider the following code. Notice anything…unusual?

init(host: String) {
        self.host = host
        self.protectionSpace = NSURLProtectionSpace(host: self.host, port: 0, `protocol`: 
            "http", realm: nil, authenticationMethod: nil)
    }

Specifically, check out those back ticks used in-line as part of the method signature. They’re required here because the word protocol, in addition to being part of the method name, is a reserved word in Swift. The back ticks enable you to differentiate reserved words and identifiers.

Having any problems in Swift getting access to native definitions through Command-click? You’re not alone. (As one person put it, “b6 is [colloquial expression of extreme disappointment] even by Xcode beta standards”) Here’s a workaround.

Select any Foundation item like NSString and Command-click it like you used to. In the definitions file, use the Jump bar to move from Foundation > NSString > NSString to Swift.

Update: If Command-Click is not working within source code, try quitting/restarting Xcode (thanks Argyrios K.). Still borked for me in Playgrounds.

This brings you to the Swift definitions you were trying to reach. Copy them to a file somewhere for easy reference.