iOS

OC对象下标索引和键索引

对于NSArray和NSDictionary我们可以通过下标直接访问对象，比如

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NSArray *arr = @[@"a", @"b", @"c"];
arr[1];   // b
NSDictionary *dic = @{@"k1": @"v1", @"k2": @"v2", @"k3": @"v3"}
dic[@"k1"];   // v1

其实对于普通NSObject类，我们通过实现一些方法也可以实现类似功能

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//实现类似数组下标索引只需实现以下方法
- (id)objectAtIndexedSubscript:(NSUInteger)idx;
- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx;

//实现类似字典键索引只需实现以下方法
- (id)objectForKeyedSubscript:(id)key;
- (void)setObject:(id)obj forKeyedSubscript:(id <NSCopying>)key;

具体使用举个例子

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/// MHKeyedSubscript.h
@interface MHKeyedSubscript : NSObject
/// 类方法
+ (instancetype) subscript;

- (id)objectForKeyedSubscript:(id)key;
- (void)setObject:(id)obj forKeyedSubscript:(id <NSCopying>)key;

- (id)objectAtIndexedSubscript:(NSUInteger)idx;
- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx;
@end

@interface MHKeyedSubscript ()
/// 字典
@property (nonatomic, readwrite, strong) NSMutableDictionary *kvs;
@end

/// MHKeyedSubscript.m
@implementation MHKeyedSubscript

+ (instancetype) subscript {
    return [[self alloc] init];
}

- (instancetype)init
{
    self = [super init];
    if (self) {
        self.kvs = [NSMutableDictionary dictionary];
    }
    return self;
}

- (id)objectForKeyedSubscript:(id)key {
    return key ? [self.kvs objectForKey:key] : nil;
}

- (void)setObject:(id)obj forKeyedSubscript:(id <NSCopying>)key {
    
    if (key) {
        if (obj) {
            [self.kvs setObject:obj forKey:key];
        } else {
            [self.kvs removeObjectForKey:key];
        }
    }
}

- (id)objectAtIndexedSubscript:(NSUInteger)idx {
    return @(idx);
}

- (void)setObject:(id)obj atIndexedSubscript:(NSUInteger)idx {
    NSLog(@"set %tu = %@", idx, obj);
}

@end
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/// ViewController.m
    MHKeyedSubscript *subscript = [MHKeyedSubscript subscript];
    subscript[0] = @"hkkb";   // set 0 = hkkb
    NSLog(@"%@", subscript[0]); // 0
    
    subscript[@"k1"] = @"v1";
    NSLog(@"k1: %@", subscript[@"k1"]); // k1: v1