Taller Swift - iCon

Fast’n Furious Introduction to
© AGBO Business Architecture S.L. Todos los derechos reservados. www.agbo.biz
Swift
Fernando Rodriguez
fernando@agbo.biz
@frr149

Objective C without the C? Not even close
Objective C
May I help you?
Swift
Could not find an overload for '/' that accepts
the supplied arguments!!!!

Objective C without the C?
• Not really…
• Much bigger language.
• Opposing philosophy: ObjC treats you as an adult, Swift behaves
as a nanny.
• Clearly influenced by C++ and Haskell.
• If you like the compiler to yell at you, you’re gonna love Swift! ;-)
• Objective C allows to go ahead without asking permission, even
though you might end up asking forgiveness.
• Swift is like a strict victorian teacher that will force you to ask
permission for everything.

Basic Building Blocks
Let’s move to the Playground…
But first, make sure you have the latest (GM) version of Xcode

Functions 101
• Functions have type too.
• And this can become confusing…
• typealias is your friend
• Parameters can have both internal and external names
• Any parameter can have a default value
• Functions can return several objects
• Pattern matching makes this very convenient
• You can’t modify an argument inside a function…unless you say
please.
• You can pass parameters by ref (InOut)

Functions 101

High Level Functions
•Functions are a type, so we should be able to manipulate them as
any other type.
•Functions as parameters to other functions.
•Functions as return values of other functions.

High Level Functions

Functions Reloaded!
•Enter the closure
•It’s a block!
•Syntax
•Capture of lexical environment
•Syntactic sugar, lotsa syntactic sugar.
Closure
"Syntactic sugar causes cancer of the semi-colons”
Alan Perlis

Functions Reloaded: Closures!

The Fear of
Nil:
Optionals

Who’s afraid of the big bad nil?
•Objective C eats raw nils everyday for breakfast.
•In Swift nils, are fearsome creatures that must be hidden inside a
box.
•This box is called an Optional.
•It can hold a nil and some other type.
•We must learn how to create optionals (put things inside the box)
•and also how to get things out of it.

Optionals

Decorators
•Decorators are functions that modify other functions.
•Common patter in other languages, such as Python.
•Decorators allow to abstract away complex and ugly code that might
not be always necessary.

Decorators

Aggregate Types
•Tuples
•Structs
•Classes
•Enums

Aggregate types
•Enums and structs are value types that are always copied, even
when assigning to a new variable.
•Beware of excessive copying, said ye olde C++ developer…
•Classes are reference types, just like in Objective C. They are
managed by ARC.
•Structs have “memberwise initialisers” by default. Classes don’t.
•Structs are widely used in Swift (Int, Array, Dictionary, etc…), and
heavily optimised by the compiler.
•Only classes have inheritance

Extending Aggregate Types
•There are 2 mechanisms:
•Inheritance (class only)
•Extensions

Inheritance
•Single inheritance only, but many protocols.
•All classes can define a super class.
•A class without a super class is considered a Base Class (like
NSObject or NSProxy in Objective C).
•Base clases actually do have a super class, called SwiftObject, but
it’s hidden.
•Swift classes are also Object C classes, so you can inherit from
NSObject (for example) in Swift.
•You can override methods and properties with override.
•You can prevent inheritance or overriding with @final.

Initialization
•Default initializer: init()
•Structs and enums can also have initialisers
•All initializers get external names by default
•Never start a parameter name with the word with. This interferes
with the way Swift interfaces with Objective C.
•Convenience initializers are prepended with the word convenience.
•Initializers are only inherited if you don’t define any designated
initialiser in the subclass.

Aggregate Types

Extensions 101
•Similar to Objective C categories, but without a name.
•Available to enums, structs and classes
•Used only to add new behaviour. Never to specialise existing
behaviour (that’s what inheritance is for).
•Unlike in Objective C, extensions are anonymous.
•Unlike in Objective C, you cant use extensions to break inheritance.
•Extensively used by Swift itself.

Extensions can
•Add computed properties
•Define instance and type methods
•Provide new convenience inits
•Make an existing type conform to a protocol
•And some other stuff too…

Extensions cannot
•Add stored properties
•Provide new designated initialisers

Extensions 101

Protocols 101
•Protocols are the entry point to extending the language.
•Extensively used by Swift itself.
•Even though protocols are implemented as a type, they can be used
as so.

Example Protocol
protocol MyProtocol: SomeProtocol, AnotherProtocol{
// Class property
class var aClassProperty: String {get}
// Instance Properties
var readWriteProperty: Int {set get}
var readOnlyProperty: String {get}
// Class Methods
class func foo() -> ()->(Bool)
// Instance Methods
func random() -> Double
}

Generics 101
•Similar to C++ templates
•Generic functions
•Generic types
•Protocol constraints on generic types

Examples
// generic function
func swap<T>(inout a: T, inout b:T)
// generic type
struct Pair<T>{
var head : T
var tail: T
}

Protocol Constraints on Generic Types
// Simple constraint
struct Pair<T: Equatable>{
var head : T
var tail: T
}
// A more complex one with ‘where’
class FooViewController<T: UIViewController
where T: UITableViewController
T: UITextFieldDelegate>{
}

Protocols & Generics

A Built-in Protocol: GeneratorType
•Generators encapsulate the creation of sets of
potentially infinite data.
•Far more powerful than iterators, as each element
can be computed on the fly.
•Generators delay unnecessary computation.
•Enormously simplify complex loops.
•First introduced by Icon.
•Can be seen as functions that preserve their state
between calls.
•This is some powerful shit!

Implemented as a protocol
protocol GeneratorType{
typealias Element
mutating func next()->Element?
}

Uses of Generators
•Recursive traversal of a directory tree
•Traversing graphs.
•Any case where getting the next element is expensive, such as:
•images processed with Core Image
•downloading data form a web server
•etc…

Generators

Another Built-in Protocol: Sequences
•Anything that can be iterated with a GeneratorType is a Sequence.
•Examples of sequences: Array, Dictionary, Range and Slice
•The for in loop uses this protocol

Another Built-in Protocol: Sequences
protocol SequenceType{
/// A type whose instances can produce the elements of this
/// sequence, in order.
typealias Generator : GeneratorType
/// Return a generator over the elements of this sequence. The
/// generator's next element is the first element of the sequence.
func generate() -> Generator
}

Homework
•Try to convert the previous generators into sequences.
•Using an infinite generator on a for loop might be…interesting. ;-)
•Look at the implementation of Array

Handling Sequences the Functional Way
• Is Swift a functional language? No, but it likes to pose as one. ;-)
• Swift has both methods and functions for handling sequences in a
functional way.
• Filter, map and reduce are all there.
• Many of these you would expect to find them as methods of the
sequence types. Instead they are implemented as global generic
functions (as in C++).

Sequences & Functional Programming

Access Control in Swift
•Not what you’re expecting…
•3 Levels of access
•Private: Entities can only be accessed from the file in which they
were defined.
•Internal: Only from the module (usually the target) where they were
defined. Default.
•Public: Accesible everywhere

Methods and Properties Private to a Class
•How do I get those?
•You don’t.
•But you can fake it with protocols and functions!

Access Control

The Road Ahead

¿Cómo sigo?
•www.keepcoding.es
•Cupón de 50% descuento icongress

GRACIAS www.agbo.biz

Taller Swift - iCon

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