我看到那些是相似的
SOCIAL_EXTERN NSString *const SLServiceTypeTwitter NS_AVAILABLE(10_8, 6_0);
SOCIAL_EXTERN NSString *const SLServiceTypeFacebook NS_AVAILABLE(10_8, 6_0);
SOCIAL_EXTERN NSString *const SLServiceTypeSinaWeibo NS_AVAILABLE(10_8, 6_0);
SOCIAL_EXTERN NSString *const SLServiceTypeTencentWeibo NS_AVAILABLE(10_9, 7_0);
SOCIAL_EXTERN NSString *const SLServiceTypeLinkedIn NS_AVAILABLE(10_9, NA);
ACCOUNTS_EXTERN NSString * const ACAccountTypeIdentifierTwitter NS_AVAILABLE(NA, 5_0);
ACCOUNTS_EXTERN NSString * const ACAccountTypeIdentifierFacebook NS_AVAILABLE(NA, 6_0);
ACCOUNTS_EXTERN NSString * const ACAccountTypeIdentifierSinaWeibo NS_AVAILABLE(NA, 6_0);
ACCOUNTS_EXTERN NSString * const ACAccountTypeIdentifierTencentWeibo NS_AVAILABLE(NA, 7_0);
ACCOUNTS_EXTERN NSString * const ACAccountTypeIdentifierLinkedIn NS_AVAILABLE(NA, NA);
为什么要跟踪两者?为什么有两组不同的常数?是否有可以将一个转换为另一个的功能,或者我应该自己制作它们?