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Grammar

This appendix presents a formal grammar for the Objective-C extensions to the C language—as the Objective-C language is implemented for the Cocoa 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

• constant

• declaration

• declaration-list

• enum-specifier

• expression

• function-definition

• identifier

• parameter-type-list

• string

• struct-declaration-list

• struct-or-union

• typedef-name

• 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 code font.

• Brackets enclose optional elements.

Otherwise, this appendix attempts to follow the conventions of The C Programming Language. Each part of the grammar consists of a symbol and a colon in bold and a 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, protocols, and blocks 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 or the symbol name ends with “-block”.

There are six entry points where the Objective-C language modifies the rules defined for standard C:

• External declarations

• Type specifiers

• Type qualifiers

• Primary expressions

• Exceptions

• Synchronization

This appendix is therefore divided into six 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.

In this section:

External Declarations
Type Specifiers
Type Qualifiers
Primary Expressions
Exceptions
Synchronization

External Declarations

• external-declaration:

• function-definition

• declaration

• class-interface

• class-implementation

• category-interface

• category-implementation

• protocol-declaration

• protocol-declaration-list

• class-declaration-list

• class-interface:

• @interfaceclass-name [ : superclass-name ]

• [ protocol-reference-list ]

• [ instance-variables ]

• [ interface-declaration-list ]

• @end

• class-implementation:

• @implementation class-name [ : superclass-name ]

• [ 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

• protocol-declaration-list:

• @protocol protocol-list ;

• 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:

• { instance-variable-declaration }

• instance-variable-declaration:

• visibility-specification

• struct-declaration-list instance-variables

• instance-variable-declaration visibility-specification

• instance-variable-declaration 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] 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

• byref

• 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 )

Exceptions

• exception-declarator:

• declarator

• try-statement:

• @trystatement

• catch-statement:

• @catch (exception-declarator)statement

• finally-statement:

• @finallystatement

• throw-statement:

• @throw (identifier)

• try-block:

• try-statement

• catch-statement

• [ finally-statement ]

Synchronization

• synchronized-statement:

• @synchronized ( identifier ) statement

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