Table showing the major translations from Objective-C to Swift syntax

Obectivej-C to Swift Syntax Translation.md

Conversion Process from Objective-C syntax to Swift The most important first step is to run Apple's "Convert to Modern Objective-C Syntax" refactoring, so that you're using array/dictionary literals and bracket-accesses; these will then be usable in Swift. Note also that I'm a beginner in Swift, so my apologies for any mistakes or incompleteness here.

When you see this pattern	Replace with this
Module
@interface *newType* : *superType* <*protocol1*, *protocol2*>	class *newType* : *superType*, *protocol1*, *protocol2*
@implementation OR @synthesize OR @end	Delete
Properties
property(…) TypeName * varName;	var varName:TypeName
property (readonly...) TypeName * varName;	let varName:TypeName
property(…) TypeName * IBOutlet varName;	@IBOutlet var varName:TypeName
_property	self.property
Compiler Directives
#import module.h	Obj-C modules: Include in ...-Bridging-Header.h Project modules: Delete Frameworks: import module
#define macroName value	let macroName = value
More complex#define / #ifdef / #ifndef	N/A
#elif value	#elseif value
#pragma mark sectionName	// MARK: sectionName (not implemented yet)
NSAssert(conditon,description)	assert(condition, description)
Types
NSString *	String
NSArray * arrayName = arrayValue	let arrayName = arrayValue OR let arrayName: Array<TypeName> = arrayValue OR let arrayName: TypeName[] = arrayValue
NSDictionary *	Dictionary
NSMutableArray OR NSMutableDictionary ...	var arrayName...
id	AnyObject
TypeName *	TypeName
c types, e.g. uint32 OR float	Titlecase , e.g. UInt32 or Float
NSInteger OR NSUInteger	Int OR UInt
Method Definitions
-(void) methodName	func methodName()
-(TypeName) methodName	func methodName() -> TypeName
-(IBAction) methodName	@IBAction func methodName
+(TypeName) methodName	class func methodName() -> TypeName
...methodName: (Type1) param1 b: (Type2) param2	...methodName(param: Type1 b param2: Typ2)
method overriden from superclass	add override
Variables
TypeName varName = value	var (OR let) name = value OR var (OR let) name: TypeName if necessary
Object Creation
TypeName * varName = [[TypeName alloc] init]	varName = TypeName()
[[TypeName alloc] initWithA: value1 B: value2]	TypeName(a: value1, b: value2)
[TypeName TypeNameWithA: value]	TypeName(a: value)
Statements
break in switch statements	not necessary, except for empty cases, but add fallthrough where needed
if/while (expr)	if/while expr, parentheses optional, but expr must now be a boolean
for ( ... )	for ..., optional
Method Calls
[object method]	object.method()
[object method: param1 b: param2 …]	object.method(param1, b: param2, …)
Expressions
YES	true
NO	false
(TypeName) value to recast	value as TypeName OR TypeName(value)
stringName.length	stringName.utf16 OR stringName.countElements
stringName isEqualToString: string2Name	stringName == string2Name
NSString stringWithFormat@"...%@..%d",obj,int)	"...\(obj)...\(int)"
Miscellaneous
semicolons at end of line	Optionally delete
@ for literals	Delete

Beyond those mostly syntactical conversions, you'll also need to do more semantic-based conversions:

• Handle all cases in switch statements (probably by adding a default case) o Add overrides for all superclass inits
• Change the definition for any variables that are only set once to let versus var
• Move getters/setters into set/get blocks in property definitions; in set, change name for the incoming value to newValue
• Biggest change is handling of nil and the new Optional types. Normal variables can no longer be assigned nil, only Optional ones. This should get rid of a vast array of program errors. On the other hand, all results from Cocoa methods are defined as Optionals with auto-unwrap. This means that the compiler will NOT warn you that the returned values are handled incorrectly, leading to a whole new set of potential runtime problems.
• For every property, either (a) assign initial value, or (b) add to init call or (c) make Optional by adding ? to type
• In initializers, you must set your own non-optional properties before calling super.init