Depending on your Object-oriented Programming background (or lack of it), you may find Logtalk nomenclature either familiar or at odds with the terms used in other languages. In addition, being a superset of Prolog, terms such as <em>predicate</em> and <em>method</em> are often used interchangeably. Logtalk inherits most of its nomenclature from Smalltalk, arguably (and somehow sadly!) not the most popular OOP language nowadays. In this section, we try to map nomenclatures from popular OOP languages such as C++ and Java to the Logtalk nomenclature.
There are several C++ glossaries available on the Internet. The list that follows relates the most commonly used C++ terms with their Logtalk equivalents.
<dd>Logtalk uses a <em>operational</em> definition of abstract class: any class that does not inherit a method for creating new instances is an abstract class. Moreover, Logtalk supports <em>interfaces</em>/<em>protocols</em>, which are often a better way to provide the functionality of C++ abstract classes.</dd>
<dd>Logtalk uses the term <em>superclass</em> with the same meaning.</dd>
</dl>
<dl>
<dt><strong>data member</strong></dt>
<dd>Logtalk uses <em>predicates</em> for representing both behavior and data.</dd>
</dl>
<dl>
<dt><strong>constructor function</strong></dt>
<dd>There are no special methods for creating new objects in Logtalk. Instead, Logtalk provides a built-in predicate, <code>create_object/4</code>, which is often used to define more sophisticated object creation predicates.</dd>
</dl>
<dl>
<dt><strong>derived class</strong></dt>
<dd>Logtalk uses the term <em>subclass</em> with the same meaning.</dd>
</dl>
<dl>
<dt><strong>destructor function</strong></dt>
<dd>There are no special methods for deleting new objects in Logtalk. Instead, Logtalk provides a built-in predicate, <code>abolish_object/1</code>, which is often used to define more sophisticated object deletion predicates.</dd>
</dl>
<dl>
<dt><strong>friend function</strong></dt>
<dd>Not supported in Logtalk. Nevertheless, see the manual section on <em>meta-predicates.</em></dd>
<dd>Logtalk uses the built-in context method <code>self/1</code> for retrieving the current instance. Logtalk also provides a <code>this/1</code> method but for returning the class containing the method being executed. Why the name clashes? Well, the notion of <em>self</em> was inherited from Smalltalk, which predates C++.</dd>
There are several Java glossaries available on the Internet. The list that follows relates the most commonly used Java terms with their Logtalk equivalents.
<dd>Logtalk uses a <em>operational</em> definition of abstract class: any class that does not inherit a method for creating new instances is an abstract class. I.e. there is no <code>abstract</code> keyword in Logtalk.</dd>
<dd>There is no <code>extends</code> keyword in Logtalk. Class inheritance is indicated using <em>specialization</em> relations. Moreover, the <em>extends</em> relation is used in Logtalk to indicate protocol or prototype extension.</dd>
<dd>Class methods may be implemented in Logtalk by using a metaclass for the class and defining the class methods in the metaclass. I.e. class methods are simply instance methods of the class metaclass.</dd>
<dd>Class variables may be implemented in Logtalk by using a metaclass for the class and defining the class variables in the class. I.e. class variables are simply instance variables of the class metaclass. Moreover, there is no <code>static</code> keyword in Logtalk.</dd>
<dd>There are no special methods for creating new objects in Logtalk. Instead, Logtalk provides a built-in predicate, <code>create_object/4</code>, which is often used to define more sophisticated object creation predicates.</dd>
<dd>Logtalk selects the method/predicate to execute in order to answer a method call based only on the method name (functor) and number of arguments (arity). Logtalk (and Prolog) are not typed languages in the same sense as Java.</dd>
<dd>Logtalk supports <em>multi-threading programming</em> in selected Prolog compilers, including a <code>synchronized/1</code> predicate directive and a <code>synchronized/0</code> object (and category) directive. Logtalk allows you to synchronize a predicate, a set of predicates, or all object predicates using per-predicate and per-object <em>locks</em>.</dd>
<dd>Logtalk uses the built-in context method <code>self/1</code> for retrieving the current instance. Logtalk also provides a <code>this/1</code> method but for returning the class containing the method being executed. Why the name clashes? Well, the notion of <em>self</em> was inherited from Smalltalk, which predates Java.</dd>
