assertz/1 — The Logtalk Handbook v3.47.0 documentation

# `assertz/1`

## Description

    assertz(Head)
    assertz((Head:-Body))

Asserts a clause as the last one for a dynamic predicate. If the predicate is not previously declared (using a scope directive), then a dynamic predicate declaration is added to the object (assuming that we are asserting locally or that the dynamic_declarations compiler flag was set to `allow` when the object was created or compiled).

When the predicate indicator for `Head` is declared in a uses/2 or use_module/2 directive, the clause is asserted in the referenced object or module. When the backend Prolog compiler supports a module system, the predicate argument can also be module qualified.

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.

## Modes and number of proofs

    assertz(+clause) - one

## 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`, `Name/Arity`, is that of a private predicate:
`permission_error(modify, private_predicate, Name/Arity)`
The predicate indicator of `Head`, `Name/Arity`, is that of a protected predicate:
`permission_error(modify, protected_predicate, Name/Arity)`
The predicate indicator of `Head`, `Name/Arity`, is that of a static predicate:
`permission_error(modify, static_predicate, Name/Arity)`
The predicate indicator of `Head`, `Name/Arity`, does not match a declared predicate and the target object was created/compiled with support for dynamic declaration of predicates turned off:
`permission_error(create, predicate_declaration, Name/Arity)`

## Examples

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

See also

abolish/1, asserta/1, clause/2, retract/1, retractall/1 dynamic/0, dynamic/1, uses/2, use_module/2