Fast enumeration

Availability

Compilers

• Clang >= 2.0

  • Apple Clang >= 1.0

  • XCode >= 3.0

• GCC >= 4.6

• GCC forks:

  • Apple GCC 4.0 build >= 5493

  • Apple GCC 4.2 build >= 5577

  • LLVM-GCC 4.2 >= 5555

Note: The feature might be available before the versions listed.

SDKs / Targets

• Mac OS X >= 10.5 Leopard

• iOS >= 3.0 (first iOS version with an SDK)

• GNUstep Base Library >= 1.21.0

Important: Fast enumeration will not work on operating systems whose collection classes do not conform to NSFastEnumeration.

Feature description

New for loop syntax:

for ( init-clause in fast-enumerator ) loop-statement

init-clause is an expression or declaration.
fast-enumerator is the object which is being iterated over which conforms to the NSFastEnumeration protocol.

For each object in fast-enumerator, the object is set equal to the object in init-clause.

An exception is raised if fast-enumerator is modified.

Otherwise, behavior is identical to a C for loop.

References

GCC documentation

The Objective-C Programming Language, “Fast Enumeration”

Programming with Objective-C, “Fast Enumeration…”

Cppreference.com – description of C for loops

NSHipster article

NSFastEnumeration protocol

typedef struct {
    unsigned long state;
    id *itemsPtr;
    unsigned long *mutationsPtr;
    unsigned long extra[5];
} NSFastEnumerationState;

@protocol NSFastEnumeration
    - (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState*) state
                                       objects: (id*) stackbuf
                                         count: (NSUInteger) len
@end

For more information, see Mike Ash’s blog post on implementing NSFastEnumeration.

References

Apple documentation

GCC documentation

Mike Ash’s blog post on implementing NSFastEnumeration