|  | 
A signal set service must meet the requirements for an I/O object service, as well as the additional requirements listed below.
        In the table below, X denotes
        a signal set service class, a
        denotes a value of type X,
        b denotes a value of type
        X::implementation_type, ec
        denotes a value of type error_code,
        n denotes a value of type
        int, and sh
        denotes a value meeting SignalHandler requirements.
      
Table 28. SignalSetService requirements
| expression | return type | 
                  assertion/note | 
|---|---|---|
| 
                   | 
                  From IoObjectService
                  requirements. | |
| 
                   | 
                  From IoObjectService
                  requirements. Implicitly clears the registered signals as if by
                  calling  | |
| 
 a.add(b, n, ec); 
 | 
                   | |
| 
 a.remove(b, n, ec); 
 | 
                   | |
| 
 a.clear(b, ec); 
 | 
                   | |
| 
 a.cancel(b, ec); 
 | 
                   | |
| 
                   | 
                   | 
                  pre:  |