クラスに [], {} を実装する ref: http://qiita.com/ezura/items/dd4ff9b0ae2a1afa3bb3

CustomClass.h

// id obj     = custom[@1];
- (id)objectForKeyedSubscript:(id)key;
// custom[@1] = @0;
- (void)setObject:(id)anObject forKeyedSubscript:(id <NSCopying>)aKey;

CustomClass.m

- (id)objectForKeyedSubscript:(id)key
{
    return @"10";
}

- (void)setObject:(id)anObject forKeyedSubscript:(id <NSCopying>)aKey
{
    ...
}

Test.m

CustomClass *custom = [CustomClass new];

id arrayObj = custom[1];
custom[0]   = @10;

id dictObj = custom[@1];
custom[@1] = @0;