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| | Pattern |
 | | Balking pattern A software design pattern balking pattern is used for computer programming. | | | State pattern A behavioral software design pattern, state pattern is used for computer programming to control the state... | | | Pattern recognition This page is about the Computer Science discipline. |
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http://www.brainyencyclopedia.com/topics/pattern.html
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| | Visitor pattern - Wikipedia, the free encyclopedia |
| | Visitor Patterns as a universal model of terminating computation. | | | In object-oriented programming and software engineering, the visitor design pattern is a way of separating an algorithm from an object structure. | | | This is the core of the matter: the Visitor abstraction emulates generic functions; the Visitor represents an algorithm. |
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http://en.wikipedia.org/wiki/Visitor_pattern
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| | Subject-oriented programming and the visitor pattern |
| | With the visitor pattern, this is done by parameterizing the recursive algorithm with an object (the visitor) implementing the processing to be performed at each node. | | | The Visitor pattern creates several redundant elements: the visitor object which must be accessed by the node, the access path by which a node finds the visitor object, and the acceptor operation which encodes the node's class in its operation name. | | | The Visitor pattern is intended to "[define a new] operation to be performed on the elements of an object structure, operation without changing the classes of the elements on which it operates" ["Design Patterns - Elements of Reusable Software" by Erich Gamma, Richard Helm, Ralph Johnson, and John Vlissides]. |
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http://www.research.ibm.com/sop/sopcvisp.htm
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| | Design Pattern Synopses |
| | The Composite pattern also allows the objects in the tree to be manipulated in a consistent manner, by requiring all of the objects in the tree to have a common superclass or interface. | | | The Strategy pattern is often used with the Null Object pattern. | | | The Null Object pattern is often used with the Strategy pattern. |
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http://www.mindspring.com/~mgrand/pattern_synopses.htm
(4381 words)
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| | Visitor Pattern |
| | The Visitor pattern is a way of packaging related operations in one place and passing that package to various elements of the system. | | | Smalltalk-80 Compiler - The visitor pattern is used for algorithms that analyze code. | | | In the absence of visitor pattern, a global variable must be provided, or an additional object must be passed to operations that perform the traversal. |
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http://pages.cpsc.ucalgary.ca/~wilkinsw/visitor/visitor.html
(3452 words)
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| | Visitor Pattern |
| | Unlike the state and strategy patterns, where a context was attached to a specific object, the visitor pattern attaches a context to a traversal. | | | Visitors group related operations performed on multiple classes (which need not be related through inheritance) together into one program component, supporting a task-based style of programming. | | | The true purpose of a visitor is to dynamically alter the implementation of one or more classes for the duration of some task. |
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http://www.ccs.neu.edu/research/demeter/papers/context-journal/node9.html
(1479 words)
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| | Visitor pattern considered useless |
| | The visitor pattern is a programming pattern that has been advocated strongly for writing code operating on a hierarchy of classes. | | | A lot of code has to be written to prepare the use of visitors: the visitor class with one abstract method per class, and a accept method per class. | | | In particular, if the hierarchy cannot be modified because you are not allowed to, the visitor pattern cannot be applied at all. |
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http://nice.sourceforge.net/visitor.html
(440 words)
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| | Visitor Pattern |
| | The purpose of the Visitor Pattern is to encapsulate an operation that you want to perform on the elements of a data structure (a class hierarchy which may not be necessarily related). | | | Using a Visitor pattern allows you to decouple the classes for the data structure and the algorithms used upon them. | | | The assumption is that you have received a fixed unrelated class hierarchy (from a vendor), which cannot be changed, and you need to add some new functionality to the hierarchy, which means that normally the base class interface needs to be changed. |
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http://www.cs.wpi.edu/~gpollice/cs509-s04/Patterns/VisitorPattern.htm
(457 words)
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| | ArticleS.UncleBob.IuseVisitor |
| | The Visitor pattern is a far better solution to this shortcoming than the naive approach using fragile chains of "instanceof" conditions. | | | An OO software developer ignoring design patterns, is akin to a crank wannabe scientist ignoring established research, you're simply wasting your own time badly reinventing the wheel. | | | A lot of the patterns arise because of the limitations of the languages used. |
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http://www.butunclebob.com/ArticleS.UncleBob.IuseVisitor
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| | Visitor Pattern |
| | So the key consideration in applying the Visitor pattern is whether you are mostly likely to change the algorithm applied over an object structure or the classes of objects that make up the structure. | | | Visitor lets you define a new operation without changing the classes of the elements on which it operates. | | | Visitors make it easy to add operations that depend on the components of complex objects. |
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http://www.swe.uni-linz.ac.at/research/deco/designPatterns/Visitor/Visitor.abstract.html
(1357 words)
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| | Visitor Design Pattern: revisited for .NET |
| | The Visitor pattern allows the developer to define new operations on the elements without changing their interface. | | | We are analyzing the pattern as originally exposed in the GoF book [1]. | | | In the Node hierarchy (that is, the original object structure), we replace all the methods with a single one, which is abstracted in an interface to be implemented in all the nodes: |
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http://weblogs.asp.net/cazzu/articles/25488.aspx
(1575 words)
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| | Visitor Pattern |
| | Visitor is easier to illustrate in code than it is to describe. | | | Visitor is in fact a "double dispatch" technique that could be used on a single object as well as a collection. | | | I wrote several visitors to load a database of links to and from my pages, build a table of contents for each page from the heading tags, ensure that the page title, page name and first heading all have the same text, and so on. |
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http://www.surfscranton.com/architecture/VisitorPattern.htm
(763 words)
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| | Applying the Visitor pattern using reflection |
| | The Visitor pattern, as defined in Design Patterns, is great if you're acting on a structure of objects in several different ways, and it makes it easy to change between the actions that you're performing on each, without having to resort to instanceof's or changing the code of the objects you act upon. | | | A limitation to the standard implementation of the pattern is that it's not suitable when the classes defining the structure itself are frequently changing, rather than the actions to be applied to them. | | | This way, you can define your visitor to accept the broadest type, rather than all the narrow types, and you can move your "accept" code into a superclass, rather than having it repeated in all of your implementations. |
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http://www.surguy.net/articles/visitor-with-reflection.xml
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| | Third Attempt: The Visitor Pattern. |
| | The Visitor pattern lets us define a new operation on an object structure without changing the classes of the objects on which it operates. | | | In summary, the Visitor pattern combines the advantages of the two other approaches. | | | Rather than writing dedicated methods for each programming task and afterwards recompiling, the idea is to (1) insert a so-called accept method in each class, and (2) write the action code in so-called visitors. |
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http://www.cs.purdue.edu/jtb/whyvisitors/node4.html
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| | Extending Behavior with the Visitor Pattern |
| | The intent of the Visitor behavior pattern is to permit you to define new operations on objects without changing the implementation of those objects. | | | Visitor uses a double dispatch mechanism so that hosts only need to define a simple Accept method that calls a Visit method on the Visitor. | | | You can define as many visitors in the future as you need without ever changing the definition of the hosts. |
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http://www.devx.com/dotnet/Article/27738/1954?pf=true
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| | Using Reflection for the Visitor Pattern - .NET Developers |
| | The visitor pattern allows you to define new, polymorphic operations on a class structure, without touching the source code for the classes themselves. | | | Unlike most other patterns books, developers will find these patterns to be universally applicable, regardless of application type or language and environment choice. | | | The patterns, sometimes referred to as the Gang of Four Patterns, or GoF patterns (so named for the book's four authors), provide the foundation for excellent modern software design. |
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http://www.dotnetdevs.com/articles/ReflectionVisitor.aspx
(1496 words)
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| | Visitor Pattern |
| | The typical example of the use of the VisitorPattern is an expression evaluator where the actual evaluation of the various operations are encapsulated in the visitor class. | | | Visitor lets you define a new operation without changing the classes of the elements on which it operates. | | | Is there anyone that could point to a situation where this pattern is being used successfully, and where it has proved to be flexible and served a useful purpose? |
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http://c2.com/cgi/wiki?VisitorPattern
(677 words)
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| | When and where to use Visitor Pattern? |
| | Visitor is a good match in that situation. | | | Using the visitor pattern, such extension could be done by defining a | | | The problem with Visitor is than it can easily be overused. |
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http://www.groupsrv.com/computers/about154317.html
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| | The Life of Riley - Visitor Pattern |
| | As part of the learning process, programmers new to the concept of patterns often try to implement them in places where they are, at best, not helpful. | | | It is not used as often as many other design patterns, and, even so, some would argue that it is overused. | | | If the algorithms applied to these items are likely to change, however, the Visitor pattern becomes a more attractive solution. |
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http://rileywhite.com/software/visitorpattern.html
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| | VisitorRevisited - The PEAK Developers' Center |
| | In addition to being useful for implementing "visitors", generic functions are a boon to any module or framework that needs to provide a facility that's open to extension, without requiring modifications to the original code. | | | The "Classic" Visitor pattern, from the Gang of Four Book, tries to solve this problem by putting the algorithm into a "Visitor" class, and using an | | | Generic functions select and execute the method with the most-specific matching condition, given the function's input parameters at runtime. |
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http://peak.telecommunity.com/DevCenter/VisitorRevisited
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| | jGuru: Visitor pattern |
| | With a Parser Code Generator like the JavaCC Parser Generator with JJTree for example a code following the visitor pattern can be generated according to a defined grammar. | | | In the software world, the Visitor patterns helps you prevent code bloat in class hierarchies, typically. | | | The classes would be changed only once, to add an "accept()" method that accept an abstract visitor object. |
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http://www.jguru.com/forums/view.jsp?EID=389160
(449 words)
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| | Hierarchical Visitor Pattern |
| | Represent an operation to be performed on the nodes of a hierarchical object structure. | | | Hierarchical Visitor lets one define new operations without changing the classes of the nodes on which it operates. | | | The members of the visitor interface are called indirectly by the implementation of accept in the Composite and Leaf classes. |
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http://c2.com/cgi/wiki?HierarchicalVisitorPattern
(2348 words)
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| | [No title] |
| | method shown above searches for a method in the visitor that matches the supplied object's type, where the notion of type is widened to include any interfaces implemented by that object. | | | For example, nodes that represent loads and stores of memory might deserve the same treatment by a given visitor. | | | The code below will find the last // interface listed for // which "this" visitor can handle the type Class iClass = nodeClass; while (ans == null && iClass != objectClass) { debugMsg("Looking for interface match in " + iClass.getName()); Class[] interfaces = iClass.getInterfaces(); for (int i = 0; i |
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http://www.cs.wustl.edu/~cytron/cs431/Current/Visitor
(1051 words)
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| | Java Tip 98: Reflect on the Visitor design pattern |
| | Unfortunately, adding new object types to a collection often requires modifying the visitor classes that have already been written. | | | Jeremy Blosser has been programming in Java for five years, during which he has worked for various software companies. | | | This article presents a more flexible approach to implementing visitors in Java, using reflection. |
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http://www.javaworld.com/javaworld/javatips/jw-javatip98.html
(1203 words)
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| | 1.12 The Visitor Pattern |
| | In this section, we introduce a design pattern, called the visitor pattern, that completely and elegantly solves the problem of adding new operations to composite class hierarchies without modifying the text of either the composite class or its variants. | | | Without access to the source code, the only way we can define new methods is to write them in procedural style as static methods in another class, losing all the benefits of object-oriented organization. | | | Moreover, we cannot use these patterns to define new operations if we do not control the source code for the composite class. |
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http://www.cs.rice.edu/~cork/newBook/node62.html
(170 words)
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| | (ootips) Visitor Pattern |
| | Design Patterns -- Elements of Reusable Object-Oriented Software | | | Rather you could use the Visitor pattern (i.e. | | | Vince Huston, A description of the Visitor pattern |
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http://ootips.org/visitor-pattern.html
(294 words)
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| | Visitor pattern |
| | I found the following web site which gives a good summary of the visitor pattern for anyone who might have missed any details during class: | | | Forum: CSCI 5161, Fall 2002, Homework 1 Discussions |
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http://www.itlabs.umn.edu/HyperNews/get/gopalan/courses/CSCI5161/Fall02/hw1/4.html
(33 words)
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| | The Visitor Pattern |
| | An example of this might be a system of Transaction objects which is fairly fixed (credit, debit, transfer, apply interest, etc.) and you are adding a lot of methods to this hierarchy as more features are required. | | | As an example of the use of the Visitor Pattern, here's some methods we could add to the system of transactions - authorization, logging, create undo state (to be used later to undo a transaction if possible). | | | Without the visitor, you would add these so called new methods into the classes that you would have been visiting. |
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http://homepage.mac.com/gordie/iblog/C1417618715/E1798042749
(280 words)
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| | SAG: Writing notes |
| | Example: This is an appropriate use of the Visitor pattern; it would be inappropriate to put the functionality directly in the tree nodes. | | | When a word or phrase set in bold or italics is followed by a punctuation mark, that mark should be set in bold or italics as well. |
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http://wiki.cs.uiuc.edu/SAG/Writing+notes
(925 words)
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| | [Tutor] Visitor Pattern |
| | I've heard that it shows how good a language is, and that Lisp is really good because it can be done in two (cryptic) lines. | | | How can a visitor pattern be implimented in Python? |
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http://mail.python.org/pipermail/tutor/2004-February/027976.html
(64 words)
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