Grammar

Reference Manual for the Objective C Language

This appendix presents a formal grammar for the Objective C extensions to the C language--as the Objective C language is implemented for the NEXTSTEP development environment. It adds to the grammar for ANSI standard C found in Appendix A of The C Programming Language (second edition, 1988) by Brian W. Kernighan and Dennis M. Ritchie, published by Prentice Hall, and should be read in conjunction with that book.
The Objective C extensions introduce some new symbols (such as class-interface), but also make use of symbols (such as function-definition) that are explained in the standard C grammar. The symbols mentioned but not explained here are listed below:

compound statement identifier

constant parameter-type-list

declaration string

declaration-list struct-declaration-list

enum-specifier struct-or-union

expression typedef-name

function-definition type-name

Of these, identifier and string are undefined terminal symbols. Objective C adds no undefined terminal symbols of its own.
Two notational conventions used here differ from those used in The C Programming Language:

Literal symbols are shown in bold type.

Brackets enclose optional elements and are in italic type. Literal brackets, like other literal symbols, are nonitalic and bold.

Otherwise, this appendix follows the conventions of the C reference manual. Each part of the grammar consists of a symbol followed by a colon and an indented list of mutually-exclusive possibilities for expanding the symbol. For example:

receiver:
expression
class-name
super

However, there is an exception: Even though they're not mutually exclusive, the constituents of classes, categories, and protocols are listed on separate lines to clearly show the ordering of elements. For example:

protocol-declaration:
@protocol protocol-name
[ protocol-reference-list ]
[ interface-declaration-list ]
@end

This exception to the general rule is easily recognized since each list terminates with @end.
There are just four entry points where the Objective C language modifies the rules defined for standard C:

External declarations

Type specifiers

Type qualifiers

Primary expressions

This appendix is therefore divided into four sections corresponding to these points. Where a rule in the standard C grammar is modified by an Objective C extension, the entire rule is repeated in its modified form.

External Declarations

external-declaration:
function-definition
declaration
class-interface
class-implementation
category-interface
category-implementation
protocol-declaration
class-declaration-list
class-interface:
@interface class-name [ : superclass-name ]
[ protocol-reference-list ]
[ instance-variables ]
[ interface-declaration-list ]
@end
class-implementation:
@implementation class-name [ : superclass-name ]
[ instance-variables ]
[ implementation-definition-list ]
@end
category-interface:
@interface class-name ( category-name )
[ protocol-reference-list ]
[ interface-declaration-list ]
@end
category-implementation:
@implementation class-name ( category-name )
[ implementation-definition-list ]
@end
protocol-declaration:
@protocol protocol-name
[ protocol-reference-list ]
[ interface-declaration-list ]
@end
class-declaration-list:
@class class-list ;
class-list:
class-name
class-list , class-name
protocol-reference-list:
< protocol-list >
protocol-list:
protocol-name
protocol-list , protocol-name
class-name:
identifier
superclass-name:
identifier
category-name:
identifier
protocol-name:
identifier
instance-variables:
{ [ visibility-specification ] struct-declaration-list [ instance-variables ] }
visibility-specification:
@private
@protected
@public
interface-declaration-list:
declaration
method-declaration
interface-declaration-list declaration
interface-declaration-list method-declaration
method-declaration:
class-method-declaration
instance-method-declaration
class-method-declaration:
+ [ method-type ] method-selector ;
instance-method-declaration:
[ method-type ] method-selector ;
implementation-definition-list:
function-definition
declaration
method-definition
implementation-definition-list function-definition
implementation-definition-list declaration
implementation-definition-list method-definition
method-definition:
class-method-definition
instance-method-definition
class-method-definition:
+ [ method-type ] method-selector [ declaration-list ] compound-statement
instance-method-definition:
[ method-type ] method-selector [ declaration-list ] compound-statement
method-selector:
unary-selector
keyword-selector [ , ... ]
keyword-selector [ , parameter-type-list ]
unary-selector:
selector
keyword-selector:
keyword-declarator
keyword-selector keyword-declarator
keyword-declarator:
: [ method-type ] identifier
selector : [ method-type ] identifier
selector:
identifier
method-type:
( type-name )

Type Specifiers

type-specifier:
void
char
short
int
long
float
double
signed
unsigned
id [ protocol-reference-list ]
class-name [ protocol-reference-list ]
struct-or-union-specifier
enum-specifier
typedef-name
struct-or-union-specifier:
struct-or-union [ identifier ] { struct-declaration-list }
struct-or-union [ identifier ] { @defs ( class-name ) }
struct-or-union identifier

Type Qualifiers

type-qualifier:
const
volatile
protocol-qualifier
protocol-qualifier:
in
out
inout
bycopy
oneway

Primary Expressions

primary-expression:
identifier
constant
string
( expression )
self
message-expression
selector-expression
protocol-expression
encode-expression
message-expression:
[ receiver message-selector ]
receiver:
expression
class-name
super
message-selector:
selector
keyword-argument-list
keyword-argument-list:
keyword-argument
keyword-argument-list keyword-argument
keyword-argument:
selector : expression
: expression
selector-expression:
@selector ( selector-name )
selector-name:
selector
keyword-name-list
keyword-name-list:
keyword-name
keyword-name-list keyword-name
keyword-name:
selector :
:
protocol-expression:
@protocol ( protocol-name )
encode-expression:
@encode ( type-name )

	compound statement	identifier
	constant	parameter-type-list
	declaration	string
	declaration-list	struct-declaration-list
	enum-specifier	struct-or-union
	expression	typedef-name
	function-definition	type-name

		Literal symbols are shown in bold type.

		Brackets enclose optional elements and are in italic type. Literal brackets, like other literal symbols, are nonitalic and bold.

		External declarations
		Type specifiers
		Type qualifiers
		Primary expressions