Basics of fast enumeration.

fast-enum-1.m

#import <Foundation/Foundation.h>

// clang -g -fobjc-arc -Weverything -framework Foundation -o fast-enum-1 fast-enum-1.m
#pragma clang diagnostic ignored "-Wobjc-missing-property-synthesis"

// --------------------------------------------------
// Pass-through

@interface Musician : NSObject
+ (id) musicianWithName: (NSString *) name  instrument: (NSString *) instrument;
@property (copy, nonatomic) NSString *name;
@property (copy, nonatomic) NSString *instrument;
@end // Musician

@implementation Musician

+ (id) musicianWithName: (NSString *) name  instrument: (NSString *) instrument {
    Musician *musician = [[self alloc] init];
    musician.name = name;
    musician.instrument = instrument;
    
    return musician;
} // musicianWithName

@end // Musician


@interface Orchestra : NSObject <NSFastEnumeration>
- (void) addMusician: (Musician *) musician;
@end // Orchestra

@implementation Orchestra {
    NSMutableArray *_members;
}

- (void) addMusician: (Musician *) musician {
    if (!_members) _members = [NSMutableArray array];
    
    [_members addObject: musician];
} // addMusician


- (NSUInteger) countByEnumeratingWithState: (NSFastEnumerationState *) enumerationState
                                   objects: (id __unsafe_unretained []) buffer 
                                     count: (NSUInteger) len {
    return [_members countByEnumeratingWithState: enumerationState
                     objects: buffer
                     count: len];
} // countByEnumeratingWithState

@end // Orchestra


int main (void) {
    @autoreleasepool {

        NSLog (@"-------------------- Fast enumeration");
        NSArray *strings =
            [NSArray arrayWithObjects: @"greeble", @"bork", @"hoover", nil];
        for (NSString *thing in strings) {
            NSLog (@"Woo! %@", thing);
        }

        NSLog (@"-------------------- Old-timey enumeration");
        NSEnumerator *enumerator = [strings objectEnumerator];
        NSString *thing;
        while ((thing = [enumerator nextObject])) {
            NSLog (@"woo.  %@", thing);
        }
        
        NSLog (@"-------------------- Reverse enumeration");
        NSEnumerator *rotaremune = [strings reverseObjectEnumerator];
        for (thing in rotaremune) {
            NSLog (@"!ooW %@", thing);
        }

        NSLog (@"-------------------- Directory enumeration");
        NSFileManager *fileManager = [NSFileManager defaultManager];
        NSDirectoryEnumerator *direnum = [fileManager enumeratorAtPath: @"/usr/share/dict"];
        NSString *filename;
        while ((filename = [direnum nextObject])) {
            NSDictionary *fileAttributes = [direnum fileAttributes];
            NSLog (@"file!  %@ : %llu", filename, [fileAttributes fileSize]);
        }
        
        NSLog (@"-------------------- Directory fast enumeration");
        direnum = [fileManager enumeratorAtPath: @"/usr/share/dict"];
        for (filename in direnum) {
            NSDictionary *fileAttributes = [direnum fileAttributes];
            NSLog (@"file!  %@ : %llu", filename, [fileAttributes fileSize]);
        }
        

        NSLog (@"-------------------- Pass-through fast enumeration");
        Orchestra *edgewoodSymphony = [[Orchestra alloc] init];
        
        Musician *peggy = [Musician musicianWithName: @"Peggy"  instrument: @"Flaut"];
        [edgewoodSymphony addMusician: peggy];
        
        Musician *jim = [Musician musicianWithName: @"Jim"  instrument: @"Bassoon"];
        [edgewoodSymphony addMusician: jim];
        
        for (Musician *member in edgewoodSymphony) {
            NSLog (@"%@ plays the %@", member.name, member.instrument);
        }

    }

    return 0;

} // main



#if 0
% clang -g -fobjc-arc -Weverything -framework Foundation -o fast-enum-1 fast-enum-1.m
% ./fast-enum-1

-------------------- Fast enumeration
Woo! greeble
Woo! bork
Woo! hoover
-------------------- Old-timey enumeration
woo.  greeble
woo.  bork
woo.  hoover
-------------------- Reverse enumeration
!ooW hoover
!ooW bork
!ooW greeble
-------------------- Directory enumeration
file!  connectives : 706
file!  propernames : 8546
file!  README : 1689
file!  web2 : 2493109
file!  web2a : 1012731
file!  words : 4
-------------------- Directory fast enumeration
file!  connectives : 706
file!  propernames : 8546
file!  README : 1689
file!  web2 : 2493109
file!  web2a : 1012731
file!  words : 4
-------------------- Pass-through fast enumeration
Peggy plays the Flaut
Jim plays the Bassoon


#endif