NSSet、NSMutableSet、NSIndexSet、NSCountedSet、NSOrderedSet、NSMutableOrderedSet类。

NSSet是不可变集合。NSSet上拥有的操作包括：比较两个集合、计算两个集合的交集和并集等。

NSMutableSet是可变集合，是NSSet的子类。NSMutableSet上拥有的操作包括：搜索、添加、删除、比较两个集合、计算两个集合的交集和并集等。

NSCountedSet用来维护对象计数。

NSIndexSet用来存储一组有序的索引，没有可变版本。

NSOrderedSet和NSMutableOrderedSet是用来处理有序、不重复集合(类似于数组)的。

示例

#import <Foundation/Foundation.h>
#import "Printing.h"

int main(int argc, const char * argv[]) {
    @autoreleasepool {
        NSMutableSet *set1 = [NSMutableSet setWithObjects:
                              @1, @3, @5, @10, nil];
        NSSet *set2 = [NSSet setWithObjects:
                       @-5, @100, @3, @5, nil];
        NSSet *set3 = [NSSet setWithObjects:
                       @12, @200, @3, nil];
        
        NSLog(@"set1: ");
        [set1 print];
        NSLog(@"set2: ");
        [set2 print];
        
        // 相等性测试
        if ([set1 isEqualToSet: set2] == YES)
            NSLog(@"set1 equals set2");
        else
            NSLog(@"set1 is not equal to set2");
        
        // 成员测试
        if ([set1 containsObject: @10] == YES)
            NSLog(@"set1 contains 10");
        else
            NSLog(@"set1 does not contain 10");
        
        if ([set2 containsObject: @10] == YES)
            NSLog(@"set2 contains 10");
        else
            NSLog(@"set2 does not contain 10");
        
        // 在可变集合set1中添加和移除对象
        [set1 addObject: @4];
        [set1 removeObject: @10];
        NSLog(@"set1 after adding 4 and removing 10: ");
        [set1 print];
        
        // 获得两个集合的交集
        [set1 intersectSet: set2];
        NSLog(@"set1 intersect set2: ");
        [set1 print];
        
        // 两个集合的并集
        [set1 unionSet: set3];
        NSLog(@"set1 union set3: ");
        [set1 print];
        
        // NSCountedSet用来记录集合中相同对象个数
        NSCountedSet *countSet = [[NSCountedSet alloc] init];
        NSLog(@"set1 count: %li", (long)[countSet countForObject: set1]);
        
        [countSet addObject: set1];
        [countSet addObject: set1];
        [countSet addObject: set1];
        
        NSLog(@"set1 count: %li", (long)[countSet countForObject: set1]);
        
        [countSet removeObject: set1];
        NSLog(@"set1 count: %li", (long)[countSet countForObject: set1]);
    }
    return 0;
}

运行测试

示例二：NSIndexSet
AddressBook.h、AddressBook.m 参见 示例：制作地址薄
添加一个查询方法

-(NSIndexSet *) lookupAll: (NSString *) theName
{
    NSIndexSet *result = [book indexesOfObjectsPassingTest:
        ^(id obj, NSUInteger idx, BOOL *stop)
        {
            if ([[obj name] caseInsensitiveCompare: theName] == NSOrderedSame)
                return YES;
            else
                return NO;
        }];
    return result;
}