Logtalk reference manual
Built-in method: asserta/1
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## asserta/1

#### Description

    asserta(Head)
    asserta((Head:-Body))

Asserts a clause as the first one for an object's dynamic predicate. If the predicate is not already declared, then a dynamic predicate declaration is added to the object (assuming that we are asserting locally or that the compiler flag `dynamic_declarations` was switched on when the object was created or compiled).

This method may be used to assert clauses for predicates that are not declared dynamic for dynamic objects provided that the predicates are declared in this. This allows easy initialization of dynamically created objects when writing constructors.

#### Template and modes

    asserta(+clause)

#### Errors

Head is a variable:
  `instantiation_error`
Head is a neither a variable nor a callable term:
  `type_error(callable, Head)`
Body cannot be converted to a goal:
  `type_error(callable, Body)`
The predicate indicator of Head, Functor/Arity, is that of a private predicate:
  `permission_error(modify, private_predicate, Functor/Arity)`
The predicate indicator of Head, Functor/Arity, is that of a protected predicate:
  `permission_error(modify, protected_predicate, Functor/Arity)`
The predicate indicator of Head, Functor/Arity, is that of a static predicate:
  `permission_error(modify, static_predicate, Functor/Arity)`
Target object was created/compiled with support for dynamic declaration of predicates turned off:
  `permission_error(create, predicate_declaration, Functor/Arity)`

#### Examples

To assert a clause as the first one for any dynamic predicate in this:
  `asserta(Clause)`
To assert a clause as the first one for any public or protected dynamic predicate in self:
  `::asserta(Clause)`
To assert a clause as the first one for any public dynamic predicate in an explicit object:
  `Object::asserta(Clause)`

#### See also

`abolish/1`, `assertz/1`, `clause/2`, `retract/1`, `retractall/1`
`dynamic/0`, `dynamic/1`