A reserved word is a term designated by the programming language that cannot be used as an identifier. This restriction is a syntactic rule that helps prevent conflicts and ambiguities in the code.

As detailed in Swift Lexical Structure, these reserved words are integral to the language’s syntax and functionality. For convenience, all lists of reserved words provided below are arranged alphabetically, facilitating quick and easy reference.

Keywords used in declarations

Keywords for defining types, methods, and essential elements in Swift, including classes, structs, enums, protocols, and properties, along with access control and initialization behavior.

Reserved Word	Details
associatedtype	Associated types are a powerful way of making protocols generic, it gives a placeholder name to a type that’s used as part of the protocol.
class	One of swift’s general purpose, flexible constructs also see struct
deinit	A method that gets automatically called when an object is freed up from memory by ARC.
enum	Enums let’s you define a custom kind of value in Swift, with predefined possible values.
extension	Extensions add new functionality to an existing class, structure, enumeration, or protocol type.
fileprivate	One of swift’s access modifiers.
func	Used for creating functions.
import	A declaration used for importing modules and submodules
init	as per swift documentation, “Initialization is the process of preparing an instance of a class, structure, or enumeration for use.”
inout	inout allows parameters to be changed outside of the function scope.
internal	One of swift’s access modifiers.
let	A keyword used for declaring a constant
open	One of swift’s access modifiers.
operator	A special symbol/ phrase that you use to check, change, or combine values.
private	One of swift’s access modifiers.
precedencegroup	defining precedence groups to use for our custom operators.
protocol	as per swift’s official documentation “A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.”
public	One of swift’s access modifiers.
rethrows	rethrows keyword is used with function that accepts a throwing function as a parameter.
static	defines a static scope.
struct	complex value-types.
subscript	Subscripts allow you to write shortcuts to elements from collections, Sequences in classes, structures and enumerations.
typealias	Defines an alias for an existing type.
var	A keyword used for declaring a variable.

Keywords used in statements

Keywords that control the flow of execution in Swift, managing loops, conditionals, error handling, and control transfer within code blocks.

Reserved Word	Details
break	One of the control transfer statements, ends execution of a loop, an if statement, or a switch statement.
case	Used for pattern testing.
catch	Used for handling any potential errors caused by a function that throws.
continue	One of the control transfer statements, ends execution of the current iteration of a loop statement but does not stop execution of the loop statement.
default	Used for default cases in switch.
defer	Used for making a block to execute just before a function exits.
do	Used for creating do blocks, for example (do-while, do-catch)
else	Used for executing a block when a condition is not satisfied.
fallthrough	One of the control transfer statements
for	Used for iterating over a sequence.
guard	Used in control transfer statement and optional unwrapping.
if	Used for condition evaluation.
in	In is a keyword defined in the Swift closure syntax as a separator between the function type and the function body in a closure, and used in checking if an object is in a sequence.
repeat	A control flow statement, similar to while loop
return	One of the control transfer statements
throw	Used for throwing an error in a function that throws.
switch	A switch statement considers a value and compares it against several possible matching patterns.
where	Used to filter out values, in statements like switch, for, protocol extension, first, contains, initializers.
while	A control flow statement, it performs a set of statements until a condition becomes false

Keywords used in expressions and types

Keywords for type casting, handling optional values, and managing Boolean literals, aiding in type checking and error handling.

Reserved Word	Details
Any	Any can represent an instance of any type at all, including function types.
as	Used for type casting.
catch	Used in error handling, when an error is thrown, it’s matched against the catch clauses.
false	A literal used to express booleans.
is	Used to check whether an object is of a certain class type
nil	A valueless state that could be assigned to optionals.
rethrows	allows forwarding a thrown error by a given function parameter
self	“self” refers to the current object within a class or struct.
Self	Refers to a type – usually the current type in the current context.
super	super is used to call up to your superclass.
throw	Used for throwing an error in a function that throws.
throws	To mark a function throwing.
true	A literal used to express booleans.
try	The try keyword is used to indicate that a method can throw an error. To catch and handle an error, the throwing method call needs to be wrapped in a do-catch statement.

Keywords used in patterns

Keywords for pattern matching and destructuring values, used in control flow statements and variable assignments.

Reserved Word
\_
.

Keywords that begin with a number sign (#), literals expressions

Compile-time literals and directives providing information about the source code, such as file names and line numbers, and controlling runtime behavior.

Reserved Word	Details
#available	Used to determine the availability of APIs at runtime
#colorLiteral	Used to make the XCode IDE to display a color swatch 🟥
#column	column number of the line where it is being run.
#dsohandle	Represents the dynamic shared object handle, which is used in low-level programming contexts, particularly when dealing with dynamic libraries. It is not commonly used in everyday Swift development.
#elseif	Literal conditional statement
#else	Literal else statement.
#endif	Literal marker for closing an a literal if statement
#error	Creates a red compiler error & prevents code from compiling
#fileID	Generates concise file string in all language modes.
#fileLiteral	Used to make the XCode IDE link to a local file.
#filePath	Outputs the file path of in which code is being run.
#file	Outputs the name of the file in which code is being run.
#function	Outputs the name of the function where code belongs.
#if	Literal if statement.
#imageLiteral	Used to make the XCode IDE to display an image.
#keyPath	Used to refer to properties in a type-safe manner, allowing for dynamic key paths in Swift. This is particularly useful in conjunction with KVO (Key-Value Observing) and other reactive programming paradigms.
#line	line number where it is being run.
#selector	Used to refer to a method that can be called by Objective-C runtime. This is essential for methods that are intended to be used as selectors in target-action patterns or notifications.
#sourceLocation	Allows developers to specify the source location for logging purposes, which can be helpful in tracing back to the original source of a log message. This can be particularly useful in large projects.
#warning	will cause Xcode to display a warning with the given message.

Keywords reserved in particular contexts

Keywords with specific meanings in certain contexts, such as defining operator behaviors, property observers, and type properties.

Reserved Word	Details
associativity	defines how operators of the same precedence are grouped together.
convenience	Convenience modifier placed before the init keyword.
didSet	A property observer
dynamic	A declaration modifier used to make use of Objective-C’s dynamism.
final	One of Swift’s access modifiers.
get	Used when getting a computed property.
indirect	Used for recursive Enums
infix	Used when creating custom operators.
lazy	Used for just-in-time calculation.
left	Used to specify the associativity of a custom operator
mutating	Functions marked as mutating can change any property within its enclosing value
none	Used to specify the associativity of a custom operator
nonmutating	Indicates that a method does not modify the instance it belongs to. This is important for maintaining immutability in certain contexts.
optional	Indicates that a value may be absent, allowing for the representation of the absence of a value in a type-safe manner. This is a core feature of Swift’s type system.
override	Used for overriding child classes.
postfix	Used in creating custom functions, it’s mathematical notation in which operators follow operands.
precedence	Operator precedence is a set of rules that determine which operator is executed before another.
prefix	Used in creating custom functions, it’s mathematical notation in which operators follow operands.
Protocol	A protocol defines a blueprint of methods, properties, and other requirements that suit a particular task or piece of functionality.
required	Required keyword means that inheriting classes must provide an implementation of the method.
right	Used to specify the associativity of a custom operator
set	Used when getting a computed property.
some	denotes an opaque type.
Type	A metatype type refers to the type of any type, including class types, structure types, enumeration types, and protocol types.
unowned	A reference type, used for memory management.
weak	A reference type, used for memory management.
willSet	A property observer

• Outside the context in which they appear in the grammar, they can be used as identifiers.

The following tokens are reserved as punctuation and can’t be used as custom operators: 

(, )	{, }	[, ]
.	,	:
;	=	@
#	& (as a prefix operator)	->
`	?	! (as a postfix operator)

Bitwise Operators in Swift

Operators for performing bit-level operations on integers, useful for low-level programming and efficient data manipulation.

Operator	Description
&	(Bitwise AND): Performs a bitwise AND operation between two integers. Each bit in the result is set to 1 if the corresponding bits of both operands are 1.
|	(Bitwise OR): Performs a bitwise OR operation between two integers. Each bit in the result is set to 1 if at least one of the corresponding bits of either operand is 1.
^	(Bitwise XOR): Performs a bitwise XOR operation between two integers. Each bit in the result is set to 1 if the corresponding bits of the operands are different.
~	(Bitwise NOT): Performs a bitwise NOT operation on a single integer. This operator inverts all the bits of the operand, turning 0s into 1s and 1s into 0s.
<<	(Left Shift): Shifts the bits of an integer to the left by a specified number of positions. This operation effectively multiplies the integer by 2 for each position shifted.
>>	(Right Shift): Shifts the bits of an integer to the right by a specified number of positions. This operation effectively divides the integer by 2 for each position shifted.
&=	(Bitwise AND Assignment): Combines the bitwise AND operation with assignment. It updates the variable by performing a bitwise AND between its current value and another value.
|=	(Bitwise OR Assignment): Combines the bitwise OR operation with assignment. It updates the variable by performing a bitwise OR between its current value and another value.
^=	(Bitwise XOR Assignment): Combines the bitwise XOR operation with assignment. It updates the variable by performing a bitwise XOR between its current value and another value.

These operators are applied to integer types (Int, UInt, etc.) and provide a way to perform efficient, low-level bit manipulation in Swift. They are especially useful in scenarios where performance and direct hardware interaction are critical.