Waqar Malik

Mix and Match

Whether you’ve decided to start a new project that uses Swift, or want to update an existing Objective-C project to use Swift, you’ll end up needing both languages in your projects. Apple calls this feature mix and match, where code written in either language can co-exist and work with the other.

Classes and Structures

Unlike in other languages, in Swift, classes and structures are very similar, with only few features that separate them. So as we describe and discuss the functionality of objects, this applies to both classes and structures. We will point out where they differ.

The Swift Playground in Xcode 6

The Swift playground is a new interactive environment in which developers can view and manipulate their code live, instead of having to continually go throught the complete compile-run-test cycle. You type your code, its evaluated, and you get feedback right away. You can see immediately whether your code is behaving as expected. Think of it as a mini project with one file and an SDK to compile against.

Interoperability with Objective-C

Swift is an awesome language and works great by itself, but when you’re writing iOS or OSX applications, you have to interface with the frameworks that Apple provides and perhaps with your own existing frameworks. You may be able to rewrite your own frameworks in Swift, but Apple has not rewritten its frameworks in Swift yet, if it ever will. Apple does provide interoperability with existing frameworks that use the Objective-C and C APIs.

Developing a Swift-Based Application

Now that you’ve learned all about Swift, let’s build an application in Swift. You’ll use most of the techniques discussed in previous chapters to develop a health-related app based on Apple’s HealthKit, a framework that allows you to store and share fitness and health data. And you’ll take advantage of HealthKit’s companion application, called Health, which can provide a quick overview of the information entered into the HealthKit database.

Memory Management and ARC

Memory management is part of a more general problem in programming called resource management. Every computer system has finite resources for a program to use. These include memory, open files, and network connections. If you use a resource, such as by opening a file, you need to clean up after yourself (in this case, by closing the file). If you keep on opening files but never close them, you’ll eventually run out of file capacity. Think about your public library. If everyone borrowed books but never returned them, eventually the library would close because it would have no more books.

Accessing Swift’s Compiler and Interpreter: REPL

Let’s now investigate how to access the Swift compiler from the command-line interface known as the Read-Eval-Print-Loop, or REPL. This is where you can interact with the compiler by entering statements, which the compiler will interpret and evaluate immediately.

Constants, Variables, and Data Types

In OOP languages, an immutable object is an object whose state can’t be modified. Swift calls these constants. Once a constant object has been created and an initial value has been assigned, the object cannot be changed. In contrast, an object whose value can be changed is a mutable object, or the object can be mutated. Swift calls these objects variables.

Introduction to Object-Oriented Programming

If you’ve been using and programming computers for any length of time, you’ve probably heard the term “object-oriented programming” more than once. Object-oriented programming, frequently shortened to its initials, OOP, is a programming technique originally developed for writing simulation programs. OOP soon caught on with developers of other kinds of software, such as those involving graphical user interfaces. Before long, “OOP” became a major industry buzzword. It promised to be the magical silver bullet that would make programming simple and joyous.

Consuming RESTful Services

If you have a Twitter account or a Facebook account, when you use their mobile applications you are consuming their services via a REST API.