The Swift lexical structure is composed of valid tokens, which serve as the fundamental building blocks that define the framework of any Swift program. These tokens encapsulate the entirety of the Swift language, establishing the syntax and semantics that govern how code is written and interpreted.
Each token can take on various forms, including identifiers, keywords, punctuation, literals, or operators, etc…
Understanding these components is essential for developers, as they form the basis for constructing meaningful and functional code. By familiarizing themselves with the different types of tokens, programmers can enhance their coding proficiency, leading to clearer, more effective communication of logic within their applications.
Swift Lexical Structure
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"
The list of basic keywords in Swift is shown below. For a comprehensive list and details, see the Swift Reserved Keywords.
| Keywords | Keywords | Keywords |
|---|---|---|
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 |
Literals
Literals in Swift fall into three categories: integer literals, floating-point literals, and string literals.
Integer Literals
var a = 10
var b = 00010100b //Binary
var c = 14x //Hexadecimal
var d = 24o //Octal
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
var a = 10.7 //Simple floating point number
var b = 10.6e2 //Exponent floating point number
var c = 10.1e-2 //Exponent floating point number
var d = 0xAp2 //Hexa decimal exponent
var d = 0xAp-2 //Hexa decimal exponent
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"
Common escape sequences include:
| Escape Sequence | Description |
|---|---|
\\0 |
Null Character |
\\ |
Backslash |
\\t |
Horizontal Tab |
\\n |
New Line |
\\r |
Carriage Return |
\\" |
Double Quote |
\\' |
Single Quote |
Operators:
Swift supports various operators, including:
| Operator | Description |
|---|---|
+ |
Addition |
- |
Subtraction |
* |
Multiplication |
/ |
Division |
% |
Remainder |
^ |
Exponent |
& |
Bitwise And |
&& |
Logical And |
| |
Bitwise Or |
|| |
Logical Or |
++ |
Increment Operator |
-- |
Decrement Operator |
~ |
Bitwise Not |
< |
Less Than |
> |
Greater Than |
... |
Etc. |
Remember, some punctuation is reserved in Swift and cannot be used as custom operators:
| Punctuation | Restrictions |
|---|---|
(, ) |
Cannot be used as custom operators |
{, } |
Cannot be used as custom operators |
[, ] |
Cannot be used as custom operators |
., , |
Cannot be used as custom operators |
:, ; |
Cannot be used as custom operators |
= |
Cannot be used as custom operators |
@, # |
Cannot be used as custom operators |
& |
Cannot be used as a prefix operator |
-> |
Cannot be used as custom operators |
` |
Cannot be used as custom operators |
?, ! |
Cannot be used as postfix operators |
Swift Whitespace
Whitespace in Swift plays a crucial role in improving code readability and structure. It is primarily used to separate tokens, ensuring that the syntax is clear and unambiguous. While whitespace can be freely used to format your code for better legibility, it is generally ignored by the Swift compiler unless it serves a syntactic purpose, such as distinguishing between prefixes or separating keywords and identifiers.
Swift Comments
Comments in Swift are essential for making your code more understandable to others (and yourself in the future). They are completely ignored by the compiler and serve purely for documentation purposes. Swift supports both single-line and multi-line comments, allowing you to annotate your code as needed:
// This is a single line comment
/* Multi line (block) comment - can have
more than one line! */