Swift Lexical Structure

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Last Updated on March 13, 2022 by Deya Eldeen

Swift lexical structure, consists of valid tokens (lowest-level building blocks) that form the structure of any swift program, these tokens describe the rest of whole swift language…

A token consists of an identifier, keyword, punctuation, literal, or operator.

1) Identifiers:
An example of an identifier is a variable name, for example here “pet” is an identifier.

let pet = "Happy Dinosaur 🦖";

Identifiers support unicode characters, you can name you variable in you native language, and as in other programming languages, you cannot use keywords as identifiers, this is still possible if you surrounding a keyword with back-ticks,

var `var` = "var"

examples of unicode identifiers are

var _latitude = 32.0;
var アップル = "apple";

2) Keywords:
The list of basic keywords in swift are listed below, see (Swift Reserved Keywords) for comprehensive list and details.

class	deinit	enum
extension	func	import
init	let	protocol
static	struct	subscript
typealias	var	break
continue	default	do
else	fallthrough	if
in	for	return
switch	where	while
as	dynamicType	is
new	super	self
Self	Type	__COLUMN__
__FILE__	__FUNCTION__	__LINE__
associativity	didSet	get
infix	inout	left
mutating	none	nonmutating
override	precedence	prefix
right	set	unowned
unowned(safe)	unowned(unsafe)	weak
willSet

3) Literals:
literals fall into 3 categories, integer, floating point, and string literals

Integer Literals
var a = 10

//Binary
var b = 00010100b

//Hexadecimal
var c = 14x

//Octal
var d = 24o

leading zeros will be ignored by the compiler, and the use of underscores is possible to increase readability.

var a = 100_000_000

Floating Point Literals
//Simple floating point number
var a = 10.7

//Exponent floating point number
var b = 10.6e2
var c = 10.1e-2
//Exponent floating point number

//Hexa decimal exponent
var d = 0xAp2

//Hexa decimal exponent
var d = 0xAp-2

String Literals

String literals are characters are enclosed within double quotes. Strings can contain escape sequences to represent characters like qoutes. Example for string literal is shown below.

var a = “test”
var a = “Hello\nWorld”

\0 Null Character
\ Backslash
\t Horizontal Tab
\n New line
\r Carriage Return
\” Double Quote
\’ Single Quote


4) Operators:
There are different operators supported in swift which includes
+ : Addition
– : Subtraction
* : Multiplication
/ : Division
% : Remainder
^ : Exponent
& : Bitwise And
&& : Logical And
| : Bitwise Or
|| : Logical Or
++ : Increment Operator
– : Minus
~ : Bitwise Not
< : Less Than
> : Greater Than
… etc.

Keep in mind, as in Swift’s official documentation, this is a list of reserved punctuation and can’t be used as custom operators:
“(, ), {, }, [, ], ., ,, :, ;, =, @, #, & (as a prefix operator), ->, `, ?, and ! (as a postfix operator)”

Swift Whitespace:
White spaces are used to separate tokens and to distinguish prefixes, otherwise it’s normally omitted by the compiler.

Swift Comments:
these are statements that are ignored by the compiler, and meant for documentation purposes of our code, they could be either one-line or multi-line.

// This is a single line comment

/* Multi line (block) comment - can have
more than one line! */