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

## implements_protocol/2-3

#### Description

    implements_protocol(Object, Protocol)
    implements_protocol(Category, Protocol)

    implements_protocol(Object, Protocol, Scope)
    implements_protocol(Category, Protocol, Scope)

Enumerates, by backtracking, all pairs of entities such that an object or a category implements a protocol. The relation scope is represented by the atoms `public`, `protected`, and `private`. This predicate only returns direct implementation relations; it does not implement a transitive closure.

#### Template and modes

    implements_protocol(?object_identifier, ?protocol_identifier)
    implements_protocol(?category_identifier, ?protocol_identifier)

    implements_protocol(?object_identifier, ?protocol_identifier, ?scope)
    implements_protocol(?category_identifier, ?protocol_identifier, ?scope)

#### Errors

Object is neither a variable nor a valid object identifier:
  `type_error(object_identifier, Object)`
Category is neither a variable nor a valid category identifier:
  `type_error(category_identifier, Category)`
Protocol is neither a variable nor a valid protocol identifier:
  `type_error(protocol_identifier, Protocol)`
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

    | ?- implements_protocol(list, listp).

    | ?- implements_protocol(list, listp, public).

#### See also

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