Visitor design pattern
The Visitor pattern separates operations on an object structure into visitor objects, allowing operations to be added without changing the structure’s element classes.
AI-Powered Developer: Build software with ChatGPT and Copilot
A visitor is an object defining operations for the concrete element types in a Visitor Pattern implementation.
- How it is used
- Separates asset-reporting operations from Asset while calculating business-line cost and depreciation totals.
- How deep it goes
- Defines Element, concrete element, Visitor, and concrete visitor roles, then shows a small stateful Python implementation.
- Examples
- Uses an IT asset-management model and a DepartmentStatisticsVisitor that totals cost, depreciation, and allocation.
- What you can do after
- Apply it via GitHub Copilot to generate a visitor that aggregates selected Asset values.
Software Design for Python Programmers
The Visitor pattern is a behavioral design pattern that separates an operation from the object structure on which it operates, allowing operations to be added without changing the structure's classes.
- How it is used
- Supports multiple algorithms making passes over one heterogeneous, often tree-shaped, data collection.
- How deep it goes
- Explains interfaces, accept traversal, runtime dispatch, concrete visitors, and a before-and-after Python refactoring.
- Examples
- Uses store products and intramural baseball, football, and volleyball games to demonstrate tree traversal and reporting visitors.
- What you can do after
- Build it from scratch by defining Node and Visitor interfaces, implementing accept dispatch, and adding independent algorithms as concrete visitors.
Read how Software Design for Python Programmers explains visitor design pattern →
Object-Oriented Software Design in C++
The Visitor Design Pattern is a behavioral design pattern that represents operations over an object structure as separate visitor objects, allowing new operations without changing the structure's element classes.
- How it is used
- Separates multiple algorithms that repeatedly process one heterogeneous, often tree-structured, data collection.
- How deep it goes
- Explains interfaces, accept traversal, type-specific visits, and a C++ refactoring, but does not discuss implementation trade-offs.
- Examples
- Uses intramural sports trees, store product trees, scores reports, activities reports, and winnings reports.
- What you can do after
- Apply via C++ interfaces and polymorphic accept methods to add independent reports without changing the tree classes.
Read how Object-Oriented Software Design in C++ explains visitor design pattern →
Fabulous Adventures in Data Structures and Algorithms
The visitor pattern separates operations on a structure from the classes representing that structure by dispatching operations through visitor objects.
- How it is used
- Separates pretty-printing logic from parse-tree classes that may also support type checking, optimization, and code generation.
- How deep it goes
- Works through a generic visitor interface and Accept implementations, including overload resolution and runtime dispatch, then applies them to document construction.
- Examples
- Uses C# expression nodes and an ExprToDoc visitor for identifiers, binary operators, member access, and calls.
- What you can do after
- Build it from scratch: add Accept dispatch to a tree and implement a separate visitor that transforms expressions into formatting documents.
Read how Fabulous Adventures in Data Structures and Algorithms explains visitor design pattern →
Related concepts
- machine learninguses · Machine learning is a field of computational methods in which systems learn patterns or relationships from data to make predictions, decisions, or other outputs.
- design patternkind of · A design pattern is a reusable, general solution structure for a recurring software design problem in a particular context.
- GitHub Copilotused by · GitHub Copilot is an AI-powered programming assistant that provides code suggestions, generation, and other software-development assistance based on prompts and programming context.
- iteratorcontrasts with · An iterator is an object or abstraction that provides successive values from a sequence or data source through a traversal protocol.
- data structureuses · A data structure is an organized representation of data and its relationships that supports defined operations for storing, accessing, or modifying it.
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