Visitor Pattern

Kind: pattern

Layer: Design Patterns Core

Record: architecture:visitor-pattern

Severity: contextual

Scope: behavior, operation, type hierarchy

Canonical: Ontology

A design pattern that places each operation over a type hierarchy in its own visitor, so an operation is added without editing the element types.

Listed in Architecture principles, after Iterator Pattern and before Memento Pattern.

Requires

• Stable Element Hierarchy

Reinforces

• Open/Closed Principle (OCP)
• Separation of Concerns

Enables

• Operation Extension Without Element Change

Conflicts with

• Type Switching

In tension with

• Element Stability

Tensions

• Visitor Pattern / Element Stability

Violated by

• Type Switching

Severity

• contextual

Category

• Behavioral Patterns

Linked from

• Core Modular Design
• SOLID / Object-Oriented Design
• Behavioral Patterns
• SOLID / Object-Oriented Design
• Severity levels
• The resolutions