Visitor pattern

Study case: employee structure

• start with a "flat" data structure
• transform it into an in-memory object tree
• add the ability to print the structure into HTML
• introduce visitor pattern
  • define traversing order
  • refactor "printing" using the visitor pattern

Data model

• Manager
  • name, profile picture
  • role
  • list of subordinaries
• Team lead
  • name, profile picture
  • list of team members
• Engineer
  • name, profile picture
  • technology

Bueno

• add external behavior without affecting the underlying data structure
• remove auxiliary behavior from the data structures

No bueno

• when a new "type" of data structure is added (or removed), all visitors have to be updated
• [if needed] visitor has to internally track the state of traversal
• exposing richer public interface

Object tree

• 12 different data types
• primitive
  • text, numeric, date, select
• composite
  • root, struct, array, array item
• dynamic
  • computed
  • reference

Visitors

• populate data structure
  • from the incoming client request
  • from the database
• finding nodes in a tree
• export(JSON)
• computing dynamic fields
• resolving references
• persisting the tree (3 variations)

I'm the last slide

Questions?