字面值

• 建立NSString、NSDictionary、NSArray、與NSNumber的不可變物件時，應使用其字面值。請特別注意， 不可將nil值放進NSArray與NSDictionary的字面值，將會導致當掉。

  NSString *pfcLongName = @"Perfect Company";
  NSArray *names = @[@"Brian", @"Matt", @"Chris", @"Alex", @"Steve", @"Paul"];
  NSDictionary *productManagers = @{@"iPhone" : @"Kate", @"iPad" : @"Kamal", @"Mobile Web" : @"Bill"};
  NSNumber *shouldUseLiterals = @YES;
  NSNumber *buildingZIPCode = @10018;