Learn swift 2 on the mac pdf

Our goals for Swift are ambitious. This documentation contains preliminary information about an API or technology in development. This information is subject to change, and software implemented according to this documentation should be tested with final operating system software. Learn more about using Apple's beta software. On This Page. Swift defines away large classes of common programming errors by adopting modern programming patterns: Variables are always initialized before use.

If we expand the Hello World folder we see that it contains a single file main. When we run this we see a notification that the build succeeded. We can see the output of our program in the console window. Or once we know the full path to it we can call it directly using the command line. The easiest way to run Swift code is using playgrounds.

Playgrounds let you interactively explore Swift code, and see it being evaluated as you enter it. Enter a name for your playground and then save it.

How to learn Swift, Apple’s language for creating iOS and macOS apps | Macworld

One the left pane you enter your Swift code. The right pane shows the result of evaluating each line of code. Whenever you enter a line in the playground, Xcode will evaluate every line in the playground, and print the result of each of these lines in the corresponding line in the right hand pane. This makes playgrounds an excellent way of getting immediate feedback on how various bits of code work.

You can just put your code in a playground and get immediate feedback on the results. The timeline view lets you examine the value of a variable over time. As you go through the following chapters, I strongly encourage you to create a playground for each chapter and enter each line of code in it and check the results.

In this chapter we introduce you to various ways to run Swift code. The different ways we covered were:. Chapter 2 Running Code The first thing you need to do with any new language is figure out how to get some code running. Apple intended Swift to support many core concepts associated with Objective-C, notably dynamic dispatch , widespread late binding , extensible programming and similar features, but in a "safer" way, making it easier to catch software bugs ; Swift has features addressing some common programming errors like null pointer dereferencing and provides syntactic sugar to help avoid the pyramid of doom.

Swift supports the concept of protocol extensibility, an extensibility system that can be applied to types, structs and classes , which Apple promotes as a real change in programming paradigms they term "protocol-oriented programming" [13] similar to traits. Initially a proprietary language , version 2.

Through version 3. Swift 4. Code written with previous versions of Swift can be updated using the migration functionality built into Xcode.


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Development of Swift started in July by Chris Lattner , with the eventual collaboration of many other programmers at Apple. Apple planned to make source code converters available if needed for the full release. Swift reached the 1. In December , IBM announced its Swift Sandbox website, which allows developers to write Swift code in one pane and display output in another. The app is presented in a 3D video game-like interface which provides feedback when lines of code are placed in a certain order and executed.

In January , Chris Lattner announced his departure from Apple for a new position with Tesla Motors , with the Swift project lead role going to team veteran Ted Kremenek. Swift is an alternative to the Objective-C language that employs modern programming-language theory concepts and strives to present a simpler syntax. During its introduction, it was described simply as "Objective-C without the C". By default, Swift does not expose pointers and other unsafe accessors , in contrast to Objective-C, which uses pointers pervasively to refer to object instances.

Also, Objective-C's use of a Smalltalk -like syntax for making method calls has been replaced with a dot-notation style and namespace system more familiar to programmers from other common object-oriented OO languages like Java or C. Swift introduces true named parameters and retains key Objective-C concepts, including protocols , closures and categories , often replacing former syntax with cleaner versions and allowing these concepts to be applied to other language structures, like enumerated types enums [43].

Under the Cocoa and Cocoa Touch environments, many common classes were part of the Foundation Kit library. Objective-C provided various bits of syntactic sugar to allow some of these objects to be created on-the-fly within the language, but once created, the objects were manipulated with object calls. In Swift, many of these basic types have been promoted to the language's core, and can be manipulated directly. Swift supports five access control levels for symbols: Unlike many object-oriented languages, these access controls ignore inheritance hierarchies: An important new feature in Swift is option types , which allow references or values to operate in a manner similar to the common pattern in C , where a pointer may refer to a value or may be null.

This implies that non-optional types cannot result in a null-pointer error ; the compiler can ensure this is not possible.

Learn Swift on the Mac

Optional types are created with the Optional mechanism—to make an Integer that is nullable, one would use a declaration similar to var optionalInteger: As in C , [46] Swift also includes syntactic sugar for this, allowing one to indicate a variable is optional by placing a question mark after the type name, var optionalInteger: Optional types wrap the base type, resulting in a different instance. String and String? To access the value inside, assuming it is not nil, it must be unwrapped to expose the instance inside. This is performed with the! In this case, the! If anOptionalInstance is nil, a null-pointer error occurs.

This can be annoying in practice, so Swift also includes the concept of optional chaining to test whether the instance is nil and then unwrap it if it is non-null:. In this case the runtime only calls someMethod if anOptionalInstance is not nil, suppressing the error. Normally this requires the programmer to test whether myValue is nil before proceeding. For instance:. Swift 2 introduced the new keyword guard for cases in which code should stop executing if some condition is unmet:. Using guard has three benefits. While the syntax can act as an if statement, its primary benefit is inferring non-nullability.

Where an if statement requires a case, guard assumes the case based on the condition provided. Also, since guard contains no scope, with exception of the else closure, leaseStart is presented as an unwrapped optional to the guard's super-scope. Lastly, if the guard statement's test fails, Swift requires the else to exit the current method or loop, ensuring leaseStart never is accessed when nil. This is performed with the keywords return , continue , break , or throw.

musings of a curious coder

Objective-C was weakly typed, and allowed any method to be called on any object at any time. If the method call failed, there was a default handler in the runtime that returned nil. That meant that no unwrapping or testing was needed, the equivalent statement in Objective-C:. However, this also demanded that all method calls be dynamic, which introduces significant overhead. Swift's use of optionals provides a similar mechanism for testing and dealing with nils, but does so in a way that allows the compiler to use static dispatch because the unwrapping action is called on a defined instance the wrapper , versus occurring in the runtime dispatch system.

In many object-oriented languages, objects are represented internally in two parts. The object is stored as a block of data placed on the heap , while the name or "handle" to that object is represented by a pointer.


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Objects are passed between methods by copying the value of the pointer, allowing the same underlying data on the heap to be accessed by anyone with a copy. In contrast, basic types like integers and floating point values are represented directly; the handle contains the data, not a pointer to it, and that data is passed directly to methods by copying. These styles of access are termed pass-by-reference in the case of objects, and pass-by-value for basic types.

Both concepts have their advantages and disadvantages. Objects are useful when the data is large, like the description of a window or the contents of a document. In these cases, access to that data is provided by copying a or bit value, versus copying an entire data structure. However, smaller values like integers are the same size as pointers typically both are one word , so there is no advantage to passing a pointer, versus passing the value. Also, pass-by-reference inherently requires a dereferencing operation, which can produce noticeable overhead in some operations, typically those used with these basic value types, like mathematics.

Similarly to C and in contrast to most other OO languages, [ citation needed ] Swift offers built-in support for objects using either pass-by-reference or pass-by-value semantics, the former using the class declaration and the latter using struct. Structs in Swift have almost all the same features as classes: For this reason, Apple terms all data generically as instances , versus objects or values.

Structs do not support inheritance, however. The programmer is free to choose which semantics are more appropriate for each data structure in the application. Larger structures like windows would be defined as classes, allowing them to be passed around as pointers. Smaller structures, like a 2D point, can be defined as structs, which will be pass-by-value and allow direct access to their internal data with no dereference.

The performance improvement inherent to the pass-by-value concept is such that Swift uses these types for almost all common data types, including Int and Double , and types normally represented by objects, like String and Array. To ensure that even the largest structs do not cause a performance penalty when they are handed off, Swift uses copy on write so that the objects are copied only if and when the program attempts to change a value in them.

This means that the various accessors have what is in effect a pointer to the same data storage, but this takes place far below the level of the language, in the computer's memory management unit MMU. So while the data is physically stored as one instance in memory, at the level of the application, these values are separate, and physical separation is enforced by copy on write only if needed.

A key feature of Objective-C is its support for categories , methods that can be added to extend classes at runtime. Categories allow extending classes in-place to add new functions with no need to subclass or even have access to the original source code. An example might be to add spell checker support to the base NSString class, which means all instances of NSString in the application gain spell checking.