Chapter 1. The Architecture of Swift

It will be useful at the outset for you to have a general sense of how the Swift language is constructed and what a Swift-based iOS program looks like. This chapter will survey the overall architecture and nature of the Swift language. Subsequent chapters will fill in the details.

Ground of Being

A complete Swift command is a statement. A Swift text file consists of multiple lines of text. Line breaks are meaningful. The typical layout of a program is one statement, one line:


(The print command provides instant feedback in the Xcode console.)

You can combine more than one statement on a line, but then you need to put a semicolon between them:

print("hello"); print("world")

You are free to put a semicolon at the end of a statement that is last or alone on its line, but no one ever does (except out of habit, because C and Objective-C require the semicolon):


Conversely, a single statement can be broken into multiple lines, to prevent long statements from becoming long lines. But you should try to do this at sensible places so as not to confuse Swift. After an opening parenthesis is a good place:


Comments are everything after two slashes in a line (so-called C++-style comments):

print("world") // this is a comment, so Swift ignores it

You can also enclose comments in /*...*/, as in C. Unlike C, C-style comments can be nested.

Many constructs in Swift use curly braces ...

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