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.

Data segment

In computing, a data segment (often denoted .data) is a portion of an object file or the corresponding virtual address space of a program that contains initialized static variables, that is, global variables and static local variables. The size of this segment is determined by the size of the values in the program's source code, and does not change at run time.

The data segment is read-write, since the values of variables can be altered at run time. This is in contrast to the read-only data segment (rodata segment or .rodata), which contains static constants rather than variables; it also contrasts to the code segment, also known as the text segment, which is read-only on many architectures. Uninitialized data, both variables and constants, is instead in the BSS segment.

Historically, to be able to support memory address spaces larger than the native size of the internal address register would allow, early CPUs implemented a system of segmentation whereby they would store a small set of indexes to use as offsets to certain areas. The Intel 8086 family of CPUs provided four segments: the code segment, the data segment, the stack segment and the extra segment. Each segment was placed at a specific location in memory by the software being executed and all instructions that operated on the data within those segments were performed relative to the start of that segment. This allowed a 16-bit address register, which would normally provide 64KiB (65536 bytes) of memory space, to access a 1MiB (1048576 bytes) address space.

Data (disambiguation)

Data is uninterpreted information.

Data or DATA may also refer to:

Music

DATA (band)

DATA were an electronic music band created in the late 1970s by Georg Kajanus, creator of such bands as Eclection, Sailor and Noir (with Tim Dry of the robotic/music duo Tik and Tok). After the break-up of Sailor in the late 1970s, Kajanus decided to experiment with electronic music and formed DATA, together with vocalists Francesca ("Frankie") and Phillipa ("Phil") Boulter, daughters of British singer John Boulter.

The classically orientated title track of DATA’s first album, Opera Electronica, was used as the theme music to the short film, Towers of Babel (1981), which was directed by Jonathan Lewis and starred Anna Quayle and Ken Campbell. Towers of Babel was nominated for a BAFTA award in 1982 and won the Silver Hugo Award for Best Short Film at the Chicago International Film Festival of the same year.

DATA released two more albums, the experimental 2-Time (1983) and the Country & Western-inspired electronica album Elegant Machinery (1985). The title of the last album was the inspiration for the name of Swedish pop synth group, elegant MACHINERY, formerly known as Pole Position.