Summary of the Grammar

Read the whole formal grammar.

Lexical Structure

Grammar of whitespace:

whitespace → whitespace-item whitespace?
whitespace-item → line-break
whitespace-item → inline-space
whitespace-item → comment
whitespace-item → multiline-comment
whitespace-item → U+0000, U+000B, or U+000C

line-break → U+000A
line-break → U+000D
line-break → U+000D followed by U+000A

inline-spaces → inline-space inline-spaces?
inline-space → U+0009 or U+0020

comment → // comment-text line-break
multiline-comment → /* multiline-comment-text */

comment-text → comment-text-item comment-text?
comment-text-item → Any Unicode scalar value except U+000A or U+000D

multiline-comment-text → multiline-comment-text-item multiline-comment-text?
multiline-comment-text-item → multiline-comment
multiline-comment-text-item → comment-text-item
multiline-comment-text-item → Any Unicode scalar value except /* or */

Grammar of an identifier:

identifier → identifier-head identifier-characters?
identifier → ` identifier-head identifier-characters? `
identifier → implicit-parameter-name
identifier → property-wrapper-projection
identifier-list → identifier | identifier , identifier-list

identifier-head → Upper- or lowercase letter A through Z
identifier-head → _
identifier-head → U+00A8, U+00AA, U+00AD, U+00AF, U+00B2–U+00B5, or U+00B7–U+00BA
identifier-head → U+00BC–U+00BE, U+00C0–U+00D6, U+00D8–U+00F6, or U+00F8–U+00FF
identifier-head → U+0100–U+02FF, U+0370–U+167F, U+1681–U+180D, or U+180F–U+1DBF
identifier-head → U+1E00–U+1FFF
identifier-head → U+200B–U+200D, U+202A–U+202E, U+203F–U+2040, U+2054, or U+2060–U+206F
identifier-head → U+2070–U+20CF, U+2100–U+218F, U+2460–U+24FF, or U+2776–U+2793
identifier-head → U+2C00–U+2DFF or U+2E80–U+2FFF
identifier-head → U+3004–U+3007, U+3021–U+302F, U+3031–U+303F, or U+3040–U+D7FF
identifier-head → U+F900–U+FD3D, U+FD40–U+FDCF, U+FDF0–U+FE1F, or U+FE30–U+FE44
identifier-head → U+FE47–U+FFFD
identifier-head → U+10000–U+1FFFD, U+20000–U+2FFFD, U+30000–U+3FFFD, or U+40000–U+4FFFD
identifier-head → U+50000–U+5FFFD, U+60000–U+6FFFD, U+70000–U+7FFFD, or U+80000–U+8FFFD
identifier-head → U+90000–U+9FFFD, U+A0000–U+AFFFD, U+B0000–U+BFFFD, or U+C0000–U+CFFFD
identifier-head → U+D0000–U+DFFFD or U+E0000–U+EFFFD

identifier-character → Digit 0 through 9
identifier-character → U+0300–U+036F, U+1DC0–U+1DFF, U+20D0–U+20FF, or U+FE20–U+FE2F
identifier-character → identifier-head
identifier-characters → identifier-character identifier-characters?

implicit-parameter-name → $ decimal-digits
property-wrapper-projection → $ identifier-characters

Grammar of a literal:

literal → numeric-literal | string-literal | regular-expression-literal | boolean-literal | nil-literal

numeric-literal → -? integer-literal | -? floating-point-literal
boolean-literal → true | false
nil-literal → nil

Grammar of an integer literal:

integer-literal → binary-literal
integer-literal → octal-literal
integer-literal → decimal-literal
integer-literal → hexadecimal-literal

binary-literal → 0b binary-digit binary-literal-characters?
binary-digit → Digit 0 or 1
binary-literal-character → binary-digit | _
binary-literal-characters → binary-literal-character binary-literal-characters?

octal-literal → 0o octal-digit octal-literal-characters?
octal-digit → Digit 0 through 7
octal-literal-character → octal-digit | _
octal-literal-characters → octal-literal-character octal-literal-characters?

decimal-literal → decimal-digit decimal-literal-characters?
decimal-digit → Digit 0 through 9
decimal-digits → decimal-digit decimal-digits?
decimal-literal-character → decimal-digit | _
decimal-literal-characters → decimal-literal-character decimal-literal-characters?

hexadecimal-literal → 0x hexadecimal-digit hexadecimal-literal-characters?
hexadecimal-digit → Digit 0 through 9, a through f, or A through F
hexadecimal-literal-character → hexadecimal-digit | _
hexadecimal-literal-characters → hexadecimal-literal-character hexadecimal-literal-characters?

Grammar of a floating-point literal:

floating-point-literal → decimal-literal decimal-fraction? decimal-exponent?
floating-point-literal → hexadecimal-literal hexadecimal-fraction? hexadecimal-exponent

decimal-fraction → . decimal-literal
decimal-exponent → floating-point-e sign? decimal-literal

hexadecimal-fraction → . hexadecimal-digit hexadecimal-literal-characters?
hexadecimal-exponent → floating-point-p sign? decimal-literal

floating-point-e → e | E
floating-point-p → p | P
sign → + | -

Grammar of a string literal:

string-literal → static-string-literal | interpolated-string-literal

string-literal-opening-delimiter → extended-string-literal-delimiter? "
string-literal-closing-delimiter → " extended-string-literal-delimiter?

static-string-literal → string-literal-opening-delimiter quoted-text? string-literal-closing-delimiter
static-string-literal → multiline-string-literal-opening-delimiter multiline-quoted-text? multiline-string-literal-closing-delimiter

multiline-string-literal-opening-delimiter → extended-string-literal-delimiter? """
multiline-string-literal-closing-delimiter → """ extended-string-literal-delimiter?
extended-string-literal-delimiter → # extended-string-literal-delimiter?

quoted-text → quoted-text-item quoted-text?
quoted-text-item → escaped-character
quoted-text-item → Any Unicode scalar value except ", \, U+000A, or U+000D

multiline-quoted-text → multiline-quoted-text-item multiline-quoted-text?
multiline-quoted-text-item → escaped-character
multiline-quoted-text-item → Any Unicode scalar value except \
multiline-quoted-text-item → escaped-newline

interpolated-string-literal → string-literal-opening-delimiter interpolated-text? string-literal-closing-delimiter
interpolated-string-literal → multiline-string-literal-opening-delimiter multiline-interpolated-text? multiline-string-literal-closing-delimiter

interpolated-text → interpolated-text-item interpolated-text?
interpolated-text-item → \( expression ) | quoted-text-item

multiline-interpolated-text → multiline-interpolated-text-item multiline-interpolated-text?
multiline-interpolated-text-item → \( expression ) | multiline-quoted-text-item

escape-sequence → \ extended-string-literal-delimiter
escaped-character → escape-sequence 0 | escape-sequence \ | escape-sequence t | escape-sequence n | escape-sequence r | escape-sequence " | escape-sequence '
escaped-character → escape-sequence u { unicode-scalar-digits }
unicode-scalar-digits → Between one and eight hexadecimal digits

escaped-newline → escape-sequence inline-spaces? line-break

Grammar of a regular expression literal:

regular-expression-literal → regular-expression-literal-opening-delimiter regular-expression regular-expression-literal-closing-delimiter
regular-expression → Any regular expression

regular-expression-literal-opening-delimiter → extended-regular-expression-literal-delimiter? /
regular-expression-literal-closing-delimiter → / extended-regular-expression-literal-delimiter?

extended-regular-expression-literal-delimiter → # extended-regular-expression-literal-delimiter?

Grammar of operators:

operator → operator-head operator-characters?
operator → dot-operator-head dot-operator-characters

operator-head → / | = | - | + | ! | * | % | < | > | & | | | ^ | ~ | ?
operator-head → U+00A1–U+00A7
operator-head → U+00A9 or U+00AB
operator-head → U+00AC or U+00AE
operator-head → U+00B0–U+00B1
operator-head → U+00B6, U+00BB, U+00BF, U+00D7, or U+00F7
operator-head → U+2016–U+2017
operator-head → U+2020–U+2027
operator-head → U+2030–U+203E
operator-head → U+2041–U+2053
operator-head → U+2055–U+205E
operator-head → U+2190–U+23FF
operator-head → U+2500–U+2775
operator-head → U+2794–U+2BFF
operator-head → U+2E00–U+2E7F
operator-head → U+3001–U+3003
operator-head → U+3008–U+3020
operator-head → U+3030

operator-character → operator-head
operator-character → U+0300–U+036F
operator-character → U+1DC0–U+1DFF
operator-character → U+20D0–U+20FF
operator-character → U+FE00–U+FE0F
operator-character → U+FE20–U+FE2F
operator-character → U+E0100–U+E01EF
operator-characters → operator-character operator-characters?

dot-operator-head → .
dot-operator-character → . | operator-character
dot-operator-characters → dot-operator-character dot-operator-characters?

infix-operator → operator
prefix-operator → operator
postfix-operator → operator

Types

Grammar of a type:

type → function-type
type → array-type
type → dictionary-type
type → type-identifier
type → tuple-type
type → optional-type
type → implicitly-unwrapped-optional-type
type → protocol-composition-type
type → opaque-type
type → metatype-type
type → any-type
type → self-type
type → ( type )

Grammar of a type annotation:

type-annotation → : attributes? inout? type

Grammar of a type identifier:

type-identifier → type-name generic-argument-clause? | type-name generic-argument-clause? . type-identifier
type-name → identifier

Grammar of a tuple type:

tuple-type → ( ) | ( tuple-type-element , tuple-type-element-list )
tuple-type-element-list → tuple-type-element | tuple-type-element , tuple-type-element-list
tuple-type-element → element-name type-annotation | type
element-name → identifier

Grammar of a function type:

function-type → attributes? function-type-argument-clause async? throws? -> type

function-type-argument-clause → ( )
function-type-argument-clause → ( function-type-argument-list ...? )

function-type-argument-list → function-type-argument | function-type-argument , function-type-argument-list
function-type-argument → attributes? inout? type | argument-label type-annotation
argument-label → identifier

Grammar of an array type:

array-type → [ type ]

Grammar of a dictionary type:

dictionary-type → [ type : type ]

Grammar of an optional type:

optional-type → type ?

Grammar of an implicitly unwrapped optional type:

implicitly-unwrapped-optional-type → type !

Grammar of a protocol composition type:

protocol-composition-type → type-identifier & protocol-composition-continuation
protocol-composition-continuation → type-identifier | protocol-composition-type

Grammar of an opaque type:

opaque-type → some type

Grammar of a boxed protocol type:

boxed-protocol-type → any type

Grammar of a metatype type:

metatype-type → type . Type | type . Protocol

Grammar of an Any type:

any-type → Any

Grammar of a Self type:

self-type → Self

Grammar of a type inheritance clause:

type-inheritance-clause → : type-inheritance-list
type-inheritance-list → attributes? type-identifier | attributes? type-identifier , type-inheritance-list

Expressions

Grammar of an expression:

expression → try-operator? await-operator? prefix-expression infix-expressions?
expression-list → expression | expression , expression-list

Grammar of a prefix expression:

prefix-expression → prefix-operator? postfix-expression
prefix-expression → in-out-expression

Grammar of an in-out expression:

in-out-expression → & primary-expression

Grammar of a try expression:

try-operator → try | try ? | try !

Grammar of an await expression:

await-operator → await

Grammar of an infix expression:

infix-expression → infix-operator prefix-expression
infix-expression → assignment-operator try-operator? await-operator? prefix-expression
infix-expression → conditional-operator try-operator? await-operator? prefix-expression
infix-expression → type-casting-operator
infix-expressions → infix-expression infix-expressions?

Grammar of an assignment operator:

assignment-operator → =

Grammar of a conditional operator:

conditional-operator → ? expression :

Grammar of a type-casting operator:

type-casting-operator → is type
type-casting-operator → as type
type-casting-operator → as ? type
type-casting-operator → as ! type

Grammar of a primary expression:

primary-expression → identifier generic-argument-clause?
primary-expression → literal-expression
primary-expression → self-expression
primary-expression → superclass-expression
primary-expression → conditional-expression
primary-expression → closure-expression
primary-expression → parenthesized-expression
primary-expression → tuple-expression
primary-expression → implicit-member-expression
primary-expression → wildcard-expression
primary-expression → macro-expansion-expression
primary-expression → key-path-expression
primary-expression → selector-expression
primary-expression → key-path-string-expression

Grammar of a literal expression:

literal-expression → literal
literal-expression → array-literal | dictionary-literal | playground-literal

array-literal → [ array-literal-items? ]
array-literal-items → array-literal-item ,? | array-literal-item , array-literal-items
array-literal-item → expression

dictionary-literal → [ dictionary-literal-items ] | [ : ]
dictionary-literal-items → dictionary-literal-item ,? | dictionary-literal-item , dictionary-literal-items
dictionary-literal-item → expression : expression

playground-literal → #colorLiteral ( red : expression , green : expression , blue : expression , alpha : expression )
playground-literal → #fileLiteral ( resourceName : expression )
playground-literal → #imageLiteral ( resourceName : expression )

Grammar of a self expression:

self-expression → self | self-method-expression | self-subscript-expression | self-initializer-expression

self-method-expression → self . identifier
self-subscript-expression → self [ function-call-argument-list ]
self-initializer-expression → self . init

Grammar of a superclass expression:

superclass-expression → superclass-method-expression | superclass-subscript-expression | superclass-initializer-expression

superclass-method-expression → super . identifier
superclass-subscript-expression → super [ function-call-argument-list ]
superclass-initializer-expression → super . init

Grammar of a conditional expression:

conditional-expression → if-expression | switch-expression

if-expression → if condition-list { statement } if-expression-tail
if-expression-tail → else if-expression
if-expression-tail → else { statement }

switch-expression → switch expression { switch-expression-cases }
switch-expression-cases → switch-expression-case switch-expression-cases?
switch-expression-case → case-label statement
switch-expression-case → default-label statement

Grammar of a closure expression:

closure-expression → { attributes? closure-signature? statements? }

closure-signature → capture-list? closure-parameter-clause async? throws? function-result? in
closure-signature → capture-list in

closure-parameter-clause → ( ) | ( closure-parameter-list ) | identifier-list
closure-parameter-list → closure-parameter | closure-parameter , closure-parameter-list
closure-parameter → closure-parameter-name type-annotation?
closure-parameter → closure-parameter-name type-annotation ...
closure-parameter-name → identifier

capture-list → [ capture-list-items ]
capture-list-items → capture-list-item | capture-list-item , capture-list-items
capture-list-item → capture-specifier? identifier
capture-list-item → capture-specifier? identifier = expression
capture-list-item → capture-specifier? self-expression
capture-specifier → weak | unowned | unowned(safe) | unowned(unsafe)

Grammar of a implicit member expression:

implicit-member-expression → . identifier
implicit-member-expression → . identifier . postfix-expression

Grammar of a parenthesized expression:

parenthesized-expression → ( expression )

Grammar of a tuple expression:

tuple-expression → ( ) | ( tuple-element , tuple-element-list )
tuple-element-list → tuple-element | tuple-element , tuple-element-list
tuple-element → expression | identifier : expression

Grammar of a wildcard expression:

wildcard-expression → _

Grammar of a macro-expansion expression:

macro-expansion-expression → # identifier generic-argument-clause? function-call-argument-clause? trailing-closures?

Grammar of a key-path expression:

key-path-expression → \ type? . key-path-components
key-path-components → key-path-component | key-path-component . key-path-components
key-path-component → identifier key-path-postfixes? | key-path-postfixes

key-path-postfixes → key-path-postfix key-path-postfixes?
key-path-postfix → ? | ! | self | [ function-call-argument-list ]

Grammar of a selector expression:

selector-expression → #selector ( expression )
selector-expression → #selector ( getter: expression )
selector-expression → #selector ( setter: expression )

Grammar of a key-path string expression:

key-path-string-expression → #keyPath ( expression )

Grammar of a postfix expression:

postfix-expression → primary-expression
postfix-expression → postfix-expression postfix-operator
postfix-expression → function-call-expression
postfix-expression → initializer-expression
postfix-expression → explicit-member-expression
postfix-expression → postfix-self-expression
postfix-expression → subscript-expression
postfix-expression → forced-value-expression
postfix-expression → optional-chaining-expression

Grammar of a function call expression:

function-call-expression → postfix-expression function-call-argument-clause
function-call-expression → postfix-expression function-call-argument-clause? trailing-closures

function-call-argument-clause → ( ) | ( function-call-argument-list )
function-call-argument-list → function-call-argument | function-call-argument , function-call-argument-list
function-call-argument → expression | identifier : expression
function-call-argument → operator | identifier : operator

trailing-closures → closure-expression labeled-trailing-closures?
labeled-trailing-closures → labeled-trailing-closure labeled-trailing-closures?
labeled-trailing-closure → identifier : closure-expression

Grammar of an initializer expression:

initializer-expression → postfix-expression . init
initializer-expression → postfix-expression . init ( argument-names )

Grammar of an explicit member expression:

explicit-member-expression → postfix-expression . decimal-digits
explicit-member-expression → postfix-expression . identifier generic-argument-clause?
explicit-member-expression → postfix-expression . identifier ( argument-names )
explicit-member-expression → postfix-expression conditional-compilation-block

argument-names → argument-name argument-names?
argument-name → identifier :

Grammar of a postfix self expression:

postfix-self-expression → postfix-expression . self

Grammar of a subscript expression:

subscript-expression → postfix-expression [ function-call-argument-list ]

Grammar of a forced-value expression:

forced-value-expression → postfix-expression !

Grammar of an optional-chaining expression:

optional-chaining-expression → postfix-expression ?

Statements

Grammar of a statement:

statement → expression ;?
statement → declaration ;?
statement → loop-statement ;?
statement → branch-statement ;?
statement → labeled-statement ;?
statement → control-transfer-statement ;?
statement → defer-statement ;?
statement → do-statement ;?
statement → compiler-control-statement
statements → statement statements?

Grammar of a loop statement:

loop-statement → for-in-statement
loop-statement → while-statement
loop-statement → repeat-while-statement

Grammar of a for-in statement:

for-in-statement → for case? pattern in expression where-clause? code-block

Grammar of a while statement:

while-statement → while condition-list code-block

condition-list → condition | condition , condition-list
condition → expression | availability-condition | case-condition | optional-binding-condition

case-condition → case pattern initializer
optional-binding-condition → let pattern initializer? | var pattern initializer?

Grammar of a repeat-while statement:

repeat-while-statement → repeat code-block while expression

Grammar of a branch statement:

branch-statement → if-statement
branch-statement → guard-statement
branch-statement → switch-statement

Grammar of an if statement:

if-statement → if condition-list code-block else-clause?
else-clause → else code-block | else if-statement

Grammar of a guard statement:

guard-statement → guard condition-list else code-block

Grammar of a switch statement:

switch-statement → switch expression { switch-cases? }
switch-cases → switch-case switch-cases?
switch-case → case-label statements
switch-case → default-label statements
switch-case → conditional-switch-case

case-label → attributes? case case-item-list :
case-item-list → pattern where-clause? | pattern where-clause? , case-item-list
default-label → attributes? default :

where-clause → where where-expression
where-expression → expression

conditional-switch-case → switch-if-directive-clause switch-elseif-directive-clauses? switch-else-directive-clause? endif-directive
switch-if-directive-clause → if-directive compilation-condition switch-cases?
switch-elseif-directive-clauses → elseif-directive-clause switch-elseif-directive-clauses?
switch-elseif-directive-clause → elseif-directive compilation-condition switch-cases?
switch-else-directive-clause → else-directive switch-cases?

Grammar of a labeled statement:

labeled-statement → statement-label loop-statement
labeled-statement → statement-label if-statement
labeled-statement → statement-label switch-statement
labeled-statement → statement-label do-statement

statement-label → label-name :
label-name → identifier

Grammar of a control transfer statement:

control-transfer-statement → break-statement
control-transfer-statement → continue-statement
control-transfer-statement → fallthrough-statement
control-transfer-statement → return-statement
control-transfer-statement → throw-statement

Grammar of a break statement:

break-statement → break label-name?

Grammar of a continue statement:

continue-statement → continue label-name?

Grammar of a fallthrough statement:

fallthrough-statement → fallthrough

Grammar of a return statement:

return-statement → return expression?

Grammar of a throw statement:

throw-statement → throw expression

Grammar of a defer statement:

defer-statement → defer code-block

Grammar of a do statement:

do-statement → do code-block catch-clauses?
catch-clauses → catch-clause catch-clauses?
catch-clause → catch catch-pattern-list? code-block
catch-pattern-list → catch-pattern | catch-pattern , catch-pattern-list
catch-pattern → pattern where-clause?

Grammar of a compiler control statement:

compiler-control-statement → conditional-compilation-block
compiler-control-statement → line-control-statement
compiler-control-statement → diagnostic-statement

Grammar of a conditional compilation block:

conditional-compilation-block → if-directive-clause elseif-directive-clauses? else-directive-clause? endif-directive

if-directive-clause → if-directive compilation-condition statements?
elseif-directive-clauses → elseif-directive-clause elseif-directive-clauses?
elseif-directive-clause → elseif-directive compilation-condition statements?
else-directive-clause → else-directive statements?
if-directive → #if
elseif-directive → #elseif
else-directive → #else
endif-directive → #endif

compilation-condition → platform-condition
compilation-condition → identifier
compilation-condition → boolean-literal
compilation-condition → ( compilation-condition )
compilation-condition → ! compilation-condition
compilation-condition → compilation-condition && compilation-condition
compilation-condition → compilation-condition || compilation-condition

platform-condition → os ( operating-system )
platform-condition → arch ( architecture )
platform-condition → swift ( >= swift-version ) | swift ( < swift-version )
platform-condition → compiler ( >= swift-version ) | compiler ( < swift-version )
platform-condition → canImport ( import-path )
platform-condition → targetEnvironment ( environment )

operating-system → macOS | iOS | watchOS | tvOS | Linux | Windows
architecture → i386 | x86_64 | arm | arm64
swift-version → decimal-digits swift-version-continuation?
swift-version-continuation → . decimal-digits swift-version-continuation?
environment → simulator | macCatalyst

Grammar of a line control statement:

line-control-statement → #sourceLocation ( file: file-path , line: line-number )
line-control-statement → #sourceLocation ( )
line-number → A decimal integer greater than zero
file-path → static-string-literal

Grammar of an availability condition:

availability-condition → #available ( availability-arguments )
availability-condition → #unavailable ( availability-arguments )
availability-arguments → availability-argument | availability-argument , availability-arguments
availability-argument → platform-name platform-version
availability-argument → *

platform-name → iOS | iOSApplicationExtension
platform-name → macOS | macOSApplicationExtension
platform-name → macCatalyst | macCatalystApplicationExtension
platform-name → watchOS | watchOSApplicationExtension
platform-name → tvOS | tvOSApplicationExtension
platform-name → visionOS
platform-version → decimal-digits
platform-version → decimal-digits . decimal-digits
platform-version → decimal-digits . decimal-digits . decimal-digits

Declarations

Grammar of a declaration:

declaration → import-declaration
declaration → constant-declaration
declaration → variable-declaration
declaration → typealias-declaration
declaration → function-declaration
declaration → enum-declaration
declaration → struct-declaration
declaration → class-declaration
declaration → actor-declaration
declaration → protocol-declaration
declaration → initializer-declaration
declaration → deinitializer-declaration
declaration → extension-declaration
declaration → subscript-declaration
declaration → operator-declaration
declaration → precedence-group-declaration \

Grammar of a top-level declaration:

top-level-declaration → statements?

Grammar of a code block:

code-block → { statements? }

Grammar of an import declaration:

import-declaration → attributes? import import-kind? import-path

import-kind → typealias | struct | class | enum | protocol | let | var | func
import-path → identifier | identifier . import-path

Grammar of a constant declaration:

constant-declaration → attributes? declaration-modifiers? let pattern-initializer-list

pattern-initializer-list → pattern-initializer | pattern-initializer , pattern-initializer-list
pattern-initializer → pattern initializer?
initializer → = expression

Grammar of a variable declaration:

variable-declaration → variable-declaration-head pattern-initializer-list
variable-declaration → variable-declaration-head variable-name type-annotation code-block
variable-declaration → variable-declaration-head variable-name type-annotation getter-setter-block
variable-declaration → variable-declaration-head variable-name type-annotation getter-setter-keyword-block
variable-declaration → variable-declaration-head variable-name initializer willSet-didSet-block
variable-declaration → variable-declaration-head variable-name type-annotation initializer? willSet-didSet-block

variable-declaration-head → attributes? declaration-modifiers? var
variable-name → identifier

getter-setter-block → code-block
getter-setter-block → { getter-clause setter-clause? }
getter-setter-block → { setter-clause getter-clause }
getter-clause → attributes? mutation-modifier? get code-block
setter-clause → attributes? mutation-modifier? set setter-name? code-block
setter-name → ( identifier )

getter-setter-keyword-block → { getter-keyword-clause setter-keyword-clause? }
getter-setter-keyword-block → { setter-keyword-clause getter-keyword-clause }
getter-keyword-clause → attributes? mutation-modifier? get
setter-keyword-clause → attributes? mutation-modifier? set

willSet-didSet-block → { willSet-clause didSet-clause? }
willSet-didSet-block → { didSet-clause willSet-clause? }
willSet-clause → attributes? willSet setter-name? code-block
didSet-clause → attributes? didSet setter-name? code-block

Grammar of a type alias declaration:

typealias-declaration → attributes? access-level-modifier? typealias typealias-name generic-parameter-clause? typealias-assignment
typealias-name → identifier
typealias-assignment → = type

Grammar of a function declaration:

function-declaration → function-head function-name generic-parameter-clause? function-signature generic-where-clause? function-body?

function-head → attributes? declaration-modifiers? func
function-name → identifier | operator

function-signature → parameter-clause async? throws? function-result?
function-signature → parameter-clause async? rethrows function-result?
function-result → -> attributes? type
function-body → code-block

parameter-clause → ( ) | ( parameter-list )
parameter-list → parameter | parameter , parameter-list
parameter → external-parameter-name? local-parameter-name parameter-type-annotation default-argument-clause?
parameter → external-parameter-name? local-parameter-name parameter-type-annotation
parameter → external-parameter-name? local-parameter-name parameter-type-annotation ...

external-parameter-name → identifier
local-parameter-name → identifier
parameter-type-annotation → : attributes? parameter-modifier? type
parameter-modifier → inout | borrowing | consuming default-argument-clause → = expression

Grammar of an enumeration declaration:

enum-declaration → attributes? access-level-modifier? union-style-enum
enum-declaration → attributes? access-level-modifier? raw-value-style-enum

union-style-enum → indirect? enum enum-name generic-parameter-clause? type-inheritance-clause? generic-where-clause? { union-style-enum-members? }
union-style-enum-members → union-style-enum-member union-style-enum-members?
union-style-enum-member → declaration | union-style-enum-case-clause | compiler-control-statement
union-style-enum-case-clause → attributes? indirect? case union-style-enum-case-list
union-style-enum-case-list → union-style-enum-case | union-style-enum-case , union-style-enum-case-list
union-style-enum-case → enum-case-name tuple-type?
enum-name → identifier
enum-case-name → identifier

raw-value-style-enum → enum enum-name generic-parameter-clause? type-inheritance-clause generic-where-clause? { raw-value-style-enum-members }
raw-value-style-enum-members → raw-value-style-enum-member raw-value-style-enum-members?
raw-value-style-enum-member → declaration | raw-value-style-enum-case-clause | compiler-control-statement
raw-value-style-enum-case-clause → attributes? case raw-value-style-enum-case-list
raw-value-style-enum-case-list → raw-value-style-enum-case | raw-value-style-enum-case , raw-value-style-enum-case-list
raw-value-style-enum-case → enum-case-name raw-value-assignment?
raw-value-assignment → = raw-value-literal
raw-value-literal → numeric-literal | static-string-literal | boolean-literal

Grammar of a structure declaration:

struct-declaration → attributes? access-level-modifier? struct struct-name generic-parameter-clause? type-inheritance-clause? generic-where-clause? struct-body
struct-name → identifier
struct-body → { struct-members? }

struct-members → struct-member struct-members?
struct-member → declaration | compiler-control-statement

Grammar of a class declaration:

class-declaration → attributes? access-level-modifier? final? class class-name generic-parameter-clause? type-inheritance-clause? generic-where-clause? class-body
class-declaration → attributes? final access-level-modifier? class class-name generic-parameter-clause? type-inheritance-clause? generic-where-clause? class-body
class-name → identifier
class-body → { class-members? }

class-members → class-member class-members?
class-member → declaration | compiler-control-statement

Grammar of an actor declaration:

actor-declaration → attributes? access-level-modifier? actor actor-name generic-parameter-clause? type-inheritance-clause? generic-where-clause? actor-body
actor-name → identifier
actor-body → { actor-members? }

actor-members → actor-member actor-members?
actor-member → declaration | compiler-control-statement

Grammar of a protocol declaration:

protocol-declaration → attributes? access-level-modifier? protocol protocol-name type-inheritance-clause? generic-where-clause? protocol-body
protocol-name → identifier
protocol-body → { protocol-members? }

protocol-members → protocol-member protocol-members?
protocol-member → protocol-member-declaration | compiler-control-statement

protocol-member-declaration → protocol-property-declaration
protocol-member-declaration → protocol-method-declaration
protocol-member-declaration → protocol-initializer-declaration
protocol-member-declaration → protocol-subscript-declaration
protocol-member-declaration → protocol-associated-type-declaration
protocol-member-declaration → typealias-declaration

Grammar of a protocol property declaration:

protocol-property-declaration → variable-declaration-head variable-name type-annotation getter-setter-keyword-block

Grammar of a protocol method declaration:

protocol-method-declaration → function-head function-name generic-parameter-clause? function-signature generic-where-clause?

Grammar of a protocol initializer declaration:

protocol-initializer-declaration → initializer-head generic-parameter-clause? parameter-clause throws? generic-where-clause?
protocol-initializer-declaration → initializer-head generic-parameter-clause? parameter-clause rethrows generic-where-clause?

Grammar of a protocol subscript declaration:

protocol-subscript-declaration → subscript-head subscript-result generic-where-clause? getter-setter-keyword-block

Grammar of a protocol associated type declaration:

protocol-associated-type-declaration → attributes? access-level-modifier? associatedtype typealias-name type-inheritance-clause? typealias-assignment? generic-where-clause?

Grammar of an initializer declaration:

initializer-declaration → initializer-head generic-parameter-clause? parameter-clause async? throws? generic-where-clause? initializer-body
initializer-declaration → initializer-head generic-parameter-clause? parameter-clause async? rethrows generic-where-clause? initializer-body
initializer-head → attributes? declaration-modifiers? init
initializer-head → attributes? declaration-modifiers? init ?
initializer-head → attributes? declaration-modifiers? init !
initializer-body → code-block

Grammar of a deinitializer declaration:

deinitializer-declaration → attributes? deinit code-block

Grammar of an extension declaration:

extension-declaration → attributes? access-level-modifier? extension type-identifier type-inheritance-clause? generic-where-clause? extension-body
extension-body → { extension-members? }

extension-members → extension-member extension-members?
extension-member → declaration | compiler-control-statement

Grammar of a subscript declaration:

subscript-declaration → subscript-head subscript-result generic-where-clause? code-block
subscript-declaration → subscript-head subscript-result generic-where-clause? getter-setter-block
subscript-declaration → subscript-head subscript-result generic-where-clause? getter-setter-keyword-block
subscript-head → attributes? declaration-modifiers? subscript generic-parameter-clause? parameter-clause
subscript-result → -> attributes? type

Grammar of a macro declaration:

macro-declaration → macro-head identifier generic-parameter-clause? macro-signature macro-definition? generic-where-clause
macro-head → attributes? declaration-modifiers? macro
macro-signature → parameter-clause macro-function-signature-result?
macro-function-signature-result → -> type
macro-definition → = expression

Grammar of an operator declaration:

operator-declaration → prefix-operator-declaration | postfix-operator-declaration | infix-operator-declaration

prefix-operator-declaration → prefix operator operator
postfix-operator-declaration → postfix operator operator
infix-operator-declaration → infix operator operator infix-operator-group?

infix-operator-group → : precedence-group-name

Grammar of a precedence group declaration:

precedence-group-declaration → precedencegroup precedence-group-name { precedence-group-attributes? }

precedence-group-attributes → precedence-group-attribute precedence-group-attributes?
precedence-group-attribute → precedence-group-relation
precedence-group-attribute → precedence-group-assignment
precedence-group-attribute → precedence-group-associativity

precedence-group-relation → higherThan : precedence-group-names
precedence-group-relation → lowerThan : precedence-group-names

precedence-group-assignment → assignment : boolean-literal

precedence-group-associativity → associativity : left
precedence-group-associativity → associativity : right
precedence-group-associativity → associativity : none

precedence-group-names → precedence-group-name | precedence-group-name , precedence-group-names
precedence-group-name → identifier

Grammar of a declaration modifier:

declaration-modifier → class | convenience | dynamic | final | infix | lazy | optional | override | postfix | prefix | required | static | unowned | unowned ( safe ) | unowned ( unsafe ) | weak
declaration-modifier → access-level-modifier
declaration-modifier → mutation-modifier
declaration-modifier → actor-isolation-modifier
declaration-modifiers → declaration-modifier declaration-modifiers?

access-level-modifier → private | private ( set )
access-level-modifier → fileprivate | fileprivate ( set )
access-level-modifier → internal | internal ( set )
access-level-modifier → public | public ( set )
access-level-modifier → open | open ( set )

mutation-modifier → mutating | nonmutating

actor-isolation-modifier → nonisolated

Attributes

Grammar of an attribute:

attribute → @ attribute-name attribute-argument-clause?
attribute-name → identifier
attribute-argument-clause → ( balanced-tokens? )
attributes → attribute attributes?

balanced-tokens → balanced-token balanced-tokens?
balanced-token → ( balanced-tokens? )
balanced-token → [ balanced-tokens? ]
balanced-token → { balanced-tokens? }
balanced-token → Any identifier, keyword, literal, or operator
balanced-token → Any punctuation except (, ), [, ], {, or }

Patterns

Grammar of a pattern:

pattern → wildcard-pattern type-annotation?
pattern → identifier-pattern type-annotation?
pattern → value-binding-pattern
pattern → tuple-pattern type-annotation?
pattern → enum-case-pattern
pattern → optional-pattern
pattern → type-casting-pattern
pattern → expression-pattern

Grammar of a wildcard pattern:

wildcard-pattern → _

Grammar of an identifier pattern:

identifier-pattern → identifier

Grammar of a value-binding pattern:

value-binding-pattern → var pattern | let pattern

Grammar of a tuple pattern:

tuple-pattern → ( tuple-pattern-element-list? )
tuple-pattern-element-list → tuple-pattern-element | tuple-pattern-element , tuple-pattern-element-list
tuple-pattern-element → pattern | identifier : pattern

Grammar of an enumeration case pattern:

enum-case-pattern → type-identifier? . enum-case-name tuple-pattern?

Grammar of an optional pattern:

optional-pattern → identifier-pattern ?

Grammar of a type casting pattern:

type-casting-pattern → is-pattern | as-pattern
is-pattern → is type
as-pattern → pattern as type

Grammar of an expression pattern:

expression-pattern → expression

Generic Parameters and Arguments

Grammar of a generic parameter clause:

generic-parameter-clause → < generic-parameter-list >
generic-parameter-list → generic-parameter | generic-parameter , generic-parameter-list
generic-parameter → type-name
generic-parameter → type-name : type-identifier
generic-parameter → type-name : protocol-composition-type

generic-where-clause → where requirement-list
requirement-list → requirement | requirement , requirement-list
requirement → conformance-requirement | same-type-requirement

conformance-requirement → type-identifier : type-identifier
conformance-requirement → type-identifier : protocol-composition-type
same-type-requirement → type-identifier == type

Grammar of a generic argument clause:

generic-argument-clause → < generic-argument-list >
generic-argument-list → generic-argument | generic-argument , generic-argument-list
generic-argument → type

Beta Software:

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 (opens in a new tab).