iOS6放出来有一段时间，添加了许多特性，其中最引人注意的是literals（简写），今天抽空整理了一下，可能不完善，聊做备忘速查只用。

• 字符串

NSNumber *theLetterZ = @'Z';
// equivalent to [NSNumber numberWithChar:'Z'];

• 整型

NSNumber *fortyTwo = @42;
// equivalent to [NSNumber numberWithInt:42];

NSNumber *fortyTwoUnsigned = @42U;
// equivalent to [NSNumber numberWithUnsignedInt:42U];

NSNumber *fortyTwoLong = @42L;
// equivalent to [NSNumber numberWithLong:42L];

NSNumber *fortyTwoLongLong = @42LL;
// equivalent to [NSNumber numberWithLongLong:42LL];

• 浮点型

NSNumber *piFloat = @3.141592654F;
// equivalent to [NSNumber numberWithFloat:3.141592654F];

NSNumber *piDouble = @3.1415926535;
// equivalent to [NSNumber numberWithDouble:3.1415926535];

• 布尔型

NSNumber *yesNumber = @YES;
// equivalent to [NSNumber numberWithBool:YES];

NSNumber *noNumber = @NO;
// equivalent to [NSNumber numberWithBool:NO];

Objective-C++ 也同样支持@true和@false

#ifdef __cplusplus
  NSNumber *trueNumber = @true;
  // equivalent to [NSNumber numberWithBool:(BOOL)true];

  NSNumber *falseNumber = @false;
  // equivalent to [NSNumber numberWithBool:(BOOL)false];
#endif

• 运算

  @( expression )

  • 数值运算

    NSNumber *smallestInt = @(-INT_MAX - 1);
    // [NSNumber numberWithInt:(-INT_MAX - 1)];
    NSNumber *piOverTwo = @(M_PI / 2);
    // [NSNumber numberWithDouble:(M_PI / 2)];
    
    

  • 枚举

    typedef enum { Red, Green, Blue } Color;
    NSNumber *favoriteColor = @(Green);
    // [NSNumber numberWithInt:((int)Green)];
    
    

  • 字符串

    NSString *path = @(getenv("PATH"));
    // [NSString stringWithUTF8String:(getenv("PATH"))];
    NSArray *pathComponents = [path componentsSeparatedByString:@":"];
    
    

  • C字符串

    NSMutableArray *args = [NSMutableArray new];
    NSMutableDictionary *options = [NSMutableDictionary new];
    while (--argc) {
      const char *arg = *++argv;
      if (strncmp(arg, "--", 2) == 0) {
          options[@(arg + 2)] = @(*++argv);  // --key value
      } else {
          [args addObject:@(arg)];            // positional argument
      }
    }
    
    

• 容器（集合）类

  • NSDictionary

    NSDictionary *dictionary = @{
    @"name" : NSUserName(),
    @"date" : [NSDate date],
    @"processInfo" : [NSProcessInfo processInfo]
    };
    NSString *str = dictionary[@"name"];
    
    

  • NSArray

    NSArray *array = @[ @"Hello", NSApp, [NSNumber numberWithInt:42] ];
    NSString *str = array[0];
    
    

  • NSMutableArray

    NSArray *array = [ @[ @"Ocarina", @"Flute", @"Harp" ] mutableCopy];
    NSString *str = array[0];
    array[0] = @“change”;
    
    

• 操作

NSMutableArray *array = ...;
NSUInteger idx = ...;
id newObject = ...;
id oldObject = array[idx];
array[idx] = newObject;           // 替换对象

NSMutableDictionary *dictionary = ...;
NSString *key = ...;
oldObject = dictionary[key];
dictionary[key] = newObject;      // 替换对象

注意事项：

1. 生成的对象都是autorelease;
2. 兼容6一下设备需进行可用性检测，以防崩溃。