The Swift Style Guide for WordPress Mobile apps

So you want to write some Swift code for WordPress apps. That’s nice, thanks a lot. But before that take some minutes to read some tips that will probably make everyone’s life easier.

First, read the Swift API Design Guidelines carefully. It’s not a long document and it establishes a common ground for what good Swift code looks like.

Our approach to building a style guide is to do it incrementally and reach consensus. You can read more about the process.

When there is not a rule for something or there’s ambiguity, you’re encouraged to create a new issue with a proposal. In the meantime, the raywenderlich.com Swift Style Guide is often a good place to look for reference, but it’s not our official guide.

Besides keeping this document short, we’re trying to organize it in two sections: a must read section for rules we can’t automatically enforce, and an all rules section as a reference of every other approved rule. You are not required to read the all rules section, as Xcode will tell you when you break those rules.

Must read

Fix all the warnings

We’re using SwiftLint to enforce as many of our rules as we can, so trust the warnings. Don’t commit or merge code with warnings. Our Release builds turn warnings into errors, so if you merge a warning you will create a problem for the person doing the release later on.

Deal with optionals early

Don't allow optional parameters just to return when they're nil.

// Correct: the return value has a chance to become non-optional.  Reduced complexity.
func process(image: UIImage) -> UIImage {
    // ...process the image...
}
let processedImage = optionalImage.map(process)

// Wrong: the return value becomes an optional as well.  Added complexity.
func process(image: UIImage?) -> UIImage? {
    guard let image == image else {
        return nil
    }

    // ...process the image...
}
let processedImage = process(optionalImage)

All the rules

Trailing new line

Files should end in one empty new line. A missing new line at the end causes trouble with diffs when the last line changes. More than one empty line is unnecessary.

Avoid trailing whitespace

There’s no need for whitespace at the end of lines and it is often the cause for unnecessary noise in diffs.

You can go to Xcode’s preferences for Text Editing and make sure both Automatically trim trailing whitespace and Including whitespace-only lines are enabled. Xcode misses some cases, but it should help a lot.

Avoid semicolons

Swift does not require a semicolon after each statement in your code. There’s no reason to add them.

Colon spacing

Colons always have no space on the left and one space on the right when specifying a type.

// Correct
let name: String
struct MyType: MyProtocol {}
func prompt<T: UIViewController>(t: T) where T: Confirmable {}

// Wrong
let name : String
struct MyType : MyProtocol {}
func prompt<T : UIViewController>(t: T) where T : Confirmable {}

Braces

Opening braces should be preceded by a single space and on the same line as the declaration. The exception to this rule is when enclosed within parentheses: no preceding space is required.

// Correct
if let myString = myString {
    print(myString)
}

struct Foo {
    let bar: String
}

foo.map({ print($0) })

// Wrong
if let myString = myString
{
    print(myString)
}

struct Foo
{
    let bar: String
}

Closing braces should always be placed on a new line regardless of the number of enclosed statements.

// Correct
guard condition else {
   return
}

// Correct
if condition { 

} else {

}

// Wrong
guard condition else { return }

// Wrong
if condition { } else { }

Commas

There should be no space before a comma and a single one after any comma.

Preferred:

function print(name: String, surname: String) {
  ...
}

Not Preferred:

function print(name: String ,surname: String) {
  ...
}

Parentheses

Parentheses around conditionals, if, for, while, do statements, are not required and should be omitted.

Preferred:

if name == "Hello" {
  print("World")
}

Not Preferred:

if (name == "Hello") {
  print("World")
}

Forced downcasts and unwrapping

Avoid using as! to force a downcast, or ! to force unwrapping. Use as? to attempt the cast, then deal with the failure case explicitly.

// Correct
func process(someObject: Any) {
    guard let element = someObject as? Element else {
        // Optional error handling goes here
        return
    }
    process(element)
}

// Wrong
func process(someObject: Any) {
    process(someObject as! Element)
}