• one blank line between methods
• whitespace around operators when defining them

Preferred

prefix operator += {}

Not Preferred

prefix operator   +-+ {}
prefix operator **    {}

• only one space between opening construct and { brace (except for compound assignment operators +=)

Preferred

func helloWorld {
 // do something
}

Not Preferred

func helloWorld{
    // do something
}

class hello     {
    var message: String
}

• one space after // in comments

Preferred

// this is a comment

Not Preferred

//this is a comment

• start and end multi-line comments with a single space

Preferred

/* This is a
multiline comment */

Not Preferred

/*This is a
multiline comment*/

• Colon directly after identifier, then space and type name

Preferred

var x: Int = 2

Not Preferred

var x : Int
var y:   String

• Colon directly after key type, then space and value for dictionary types

Preferred

var x = [ 'key1': 1, 'key2': 2 ]
var y: [ Int: String ]

Not Preferred

var x = [ 'key1' : 1, 'key2':  3]
var y: [ Int :    String ]

• Colon directly after case label, then space and statements

Preferred

switch character {
case "a": doSomething(a);
default: alert();
}

Not Preferred

switch character {
case "a" : doSomething(a);
default:     alert();
}

• Colon directly after class/struct/protocol/extension name, followed by space, followed by type inheritance list

Preferred

class ClassName: BaseClass {
}

struct StructName: BaseStruct {
}

protocol ProtocolName: AnotherProtocol {
}

extension TypeName: ProtocolName {
}

Not Preferred

class ClassName : BaseClass {
}

struct StructName:  BaseStruct {
}

protocol ProtocolName:AnotherProtocol {
}

extension TypeName : ProtocolName {
}

• Single space before and after colon in a conditional expression

Preferred

var x = condition ? a : b

Not Preferred

var x = condition ? a: b
var x = condition ? a   : b

• Tuple name, followed by colon, followed by a space, followed by value

Preferred

var y = (key: 1, value: 2)

Not Preferred

var y = (key:1, value : 2)

• Colon directly after typeName, followed by a space in generic parameter clauses

Preferred

func someFunction<T: SomeClass, U: SomeProtocol>(someT: T, someU: U) {
}

Not Preferred

func someFunction<T : SomeClass, U:SomeProtocol>(someT: T, someU: U) {
}

• Check for a space before and after '->' in function and closure declarations
• Check for a space before and after '->' in subscripts
• Check for a space before and after '->' in function types