Logtalk reference manual
Built-in predicate: extends_protocol/2-3
Contents > Reference Manual > Built-in Predicates > extends_protocol/2-3

## extends_protocol/2-3

#### Description

    extends_protocol(Protocol1, Protocol2)
    extends_protocol(Protocol1, Protocol2, Scope)

Enumerates, by backtracking, all pairs of protocols such that the first one extends the second. The relation scope is represented by the atoms `public`, `protected`, and `private`.

#### Template and modes

    extends_protocol(?protocol_identifier, ?protocol_identifier)
    extends_protocol(?protocol_identifier, ?protocol_identifier, ?scope)

#### Errors

Protocol1 is neither a variable nor a valid protocol identifier:
  `type_error(protocol_identifier, Protocol1)`
Protocol2 is neither a variable nor a valid protocol identifier:
  `type_error(protocol_identifier, Protocol2)`
Scope is neither a variable nor an atom:
  `type_error(atom, Scope)`
Scope is an atom but an invalid entity scope:
  `domain_error(scope, Scope)`

#### Examples

    | ?- extends_protocol(listp, Protocol).

    | ?- extends_protocol(Protocol, termp, private).

#### See also

`current_protocol/1`, `implements_protocol/2-3`, `conforms_to_protocol/2-3`