A guide to our Swift style and conventions.

This is an attempt to encourage patterns that accomplish the following goals (in rough priority order):

1. Increased rigor, and decreased likelihood of programmer error
2. Increased clarity of intent
3. Reduced verbosity
4. Fewer debates about aesthetics

If you have suggestions, please see our contribution guidelines, then open a pull request. ⚡

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Whitespace

• Tabs, not spaces.
• End files with a newline.
• Make liberal use of vertical whitespace to divide code into logical chunks.
• Don’t leave trailing whitespace.
  • Not even leading indentation on blank lines.

Prefer implicit getters on read-only properties and subscripts

When possible, omit the get keyword on read-only computed properties and read-only subscripts.

So, write these:

var myGreatProperty: Int {
	return 4
}

subscript(index: Int) -> T {
    return objects[index]
}

… not these:

var myGreatProperty: Int {
	get {
		return 4
	}
}

subscript(index: Int) -> T {
    get {
        return objects[index]
    }
}

Rationale: The intent and meaning of the first version is clear, and results in less code.

Always specify access control explicitly for top-level definitions

Top-level functions, types, and variables should always have explicit access control specifiers:

public var whoopsGlobalState: Int
internal struct TheFez {}
private func doTheThings(things: [Thing]) {}

However, definitions within those can leave access control implicit, where appropriate:

internal struct TheFez {
	var owner: Person = Joshaber()
}

Rationale: It's rarely appropriate for top-level definitions to be specifically internal, and being explicit ensures that careful thought goes into that decision. Within a definition, reusing the same access control specifier is just duplicative, and the default is usually reasonable.

When specifying a type, always associate the colon with the identifier

When specifying the type of an identifier, always put the colon immediately after the identifier, followed by a space and then the type name.

class SmallBatchSustainableFairtrade: Coffee { ... }

let timeToCoffee: NSTimeInterval = 2

func makeCoffee(type: CoffeeType) -> Coffee { ... }

Rationale: The type specifier is saying something about the identifier so it should be positioned with it.

Only explicitly refer to self when required

When accessing properties or methods on self, leave the reference to self implicit by default:

private class History {
	var events: [Event]

	func rewrite() {
		events = []
	}
}

Only include the explicit keyword when required by the language—for example, in a closure, or when parameter names conflict:

extension History {
	init(events: [Event]) {
		self.events = events
	}

	var whenVictorious: () -> () {
		return {
			self.rewrite()
		}
	}
}

Rationale: This makes the capturing semantics of self stand out more in closures, and avoids verbosity elsewhere.

Prefer structs over classes