Visitor pattern

In object-oriented programming and software engineering, the visitor design pattern is a way of separating an algorithm from an object structure on which it operates. A practical result of this separation is the ability to add new operations to existing object structures without modifying those structures. It is one way to follow the open/closed principle.

In essence, the visitor allows one to add new virtual functions to a family of classes without modifying the classes themselves; instead, one creates a visitor class that implements all of the appropriate specializations of the virtual function. The visitor takes the instance reference as input, and implements the goal through double dispatch.

Definition

The Gang of Four defines the Visitor as:

The nature of the Visitor makes it an ideal pattern to plug into public APIs thus allowing its clients to perform operations on a class using a “visiting” class without having to modify the source.

Motivation

Consider the design of a 2D CAD system. At its core there are several types to represent basic geometric shapes like circles, lines and arcs. The entities are ordered into layers, and at the top of the type hierarchy is the drawing, which is simply a list of layers, plus some additional properties.

Visitor (album)

The first full-length album by American artist onelinedrawing.

Track listing

Writing credits

All songs by Jonah Matranga.

Visitor (disambiguation)

A visitor is someone who comes to a place for a short period of time

In English and Welsh law, Visitor is an academic or ecclesiastical title

Visitor or Visitors may also refer to:

Film

Literature

Avenger

Avenger may refer to:

Aircraft

Military

Warships

Vehicles

Avenger (British band)

Avenger are a heavy metal band from Newcastle, England. Associated with the New Wave of British Heavy Metal scene, they released two albums in the 1980s before splitting up. The band reunited in 2005.

History

Brian Ross, Mick Moore and Gary Young founded Avenger late in 1982 after Ross and Moore's previous group, Blitzkrieg, split up. the group began recording demos, "Hot 'n' Heavy Express", was their first appearance on record, included on a Neat Records compilation EP. Their debut single for Neat, "Too Wild to Tame", followed in October 1983 after the addition of guitarist John Brownless.

Shortly after this, lead singer Brian Ross left the group to join Satan; Satan's singer, Ian Swift, promptly joined Avenger as lead vocalist. Adding guitarist Les Cheetham, they released their first LP, Blood Sports, in 1984. This began a period of the band playing regularly in western Europe at the time a hub of the emerging metal scene

A second album followed shortly after on Neat, entitled Killer Elite along with a three track accompanying video. The group toured the United States in 1986. replacing Les Cheetam with Greg Reiter, The touring duty of the US tour fell to Darren Kurland as drummer . After 4 months returning to England the group broke up, blaming poor record label support preventing the band exploiting their potential in America. Ian Swift joining Atomkraft and Gary later joining Blitzkrieg.

Way of the Tiger

The Way of the Tiger is the name of a series of adventure gamebooks by Mark Smith and Jamie Thomson set on the fantasy world of Orb. The reader takes the part of a young monk-ninja, Avenger, on his quest to avenge his foster father and recover the Scrolls of Kettsuin. Later books present fresh challenges for Avenger to overcome.

The world of Orb was originally drawn up by Mark Smith for a Dungeons and Dragons game he dungeon-mastered while a pupil at Brighton College in the mid-1970s. Orb was also used as the setting for the Fighting Fantasy gamebook Talisman of Death, again by Smith & Thomson.

Each book has a disclaimer at the front against performing any of the ninja related feats in the book as "They could lead to serious injury or death to an untrained user".

The sixth book, Inferno!, ends on a cliffhanger with Avenger trapped in the web of the Black Widow, Orb's darkest blight. As no new books were released, the fate of Avenger and Orb was unknown. Mark Smith has confirmed that the cliffhanger ending was deliberate.