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 (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

Smallville (season 2)

Season two of Smallville, an American television series developed by Alfred Gough and Miles Millar, began airing on September 24, 2002, on The WB television network. The series recounts the early adventures of Kryptonian Clark Kent as he adjusts to life in the fictional town of Smallville, Kansas, during the years before he becomes Superman. The second season comprises 23 episodes and concluded its initial airing on May 20, 2003. Regular cast members during season two include Tom Welling, Kristin Kreuk, Michael Rosenbaum, Sam Jones III, Allison Mack, Annette O'Toole and John Schneider. John Glover who was a recurring guest in season one was promoted to regular for season two. At the end of season one, Eric Johnson, who portrayed Whitney Fordman, had left the show.

Season two picks up directly where season one ended, with Clark (Welling) dealing with the aftermath of the tornadoes that hit Smallville. This season, Clark finally learns who he is and where he comes from, but must also acknowledge a potential destiny set into motion by his biological father that could change his life and the lives of those around him forever. Clark's relationship with Lana Lang (Kreuk) becomes increasingly closer, straining his friendship with Chloe Sullivan (Mack). Clark's best friend, Pete Ross (Jones III), learns Clark's secret this season.

Hey

Hey or Hey! may refer to:

Interjection

Music

Albums

Songs

Hey! (Julio Iglesias album)

Hey! is an album by Julio Iglesias. It was released in 1980 by Columbia Records. The album hit number one worldwide, and sales of the Spanish version purportedly surpassed 20 million. In 1981, Iglesias was nominated for a Grammy Award for the album under the Latin Pop Album category.

Track listing

Sales and certifications

References

External links

Hey! (Jullie album)

Hey! is the debut studio album by Brazilian recording artist Jullie. It was released on September 22, 2009 by Deckdisc. After writing songs for several established acts, Jullie released this album. The main theme of the songs is girl power. The songs are mostly inspired by Jullie's love of youth, rebellion, and discover who you are in 4.modern lifestyle. Musically, the album drew inspiration from pop and pop rock influenced by singers like Lily Allen, Madonna, Alanis Morissette, and its main reference, Katy Perry, directed to a feminist position. The album was praised by the young, calling Jullie as "Brazilian Katy Perry" for his music style and way of dressing. The first single "Alice" was released in April and the second single "Hey!" was released in November, 2009.

Track listing

References

External links