2015
Pluralsight
Zoran Horvat
4:49
English

Textbooks and courses explain a design pattern by highlighting a situation, then providing a convenient solution: the pattern. There is nothing wrong with this when documenting a design pattern. The problem comes when the same sequence of steps is applied to recognize the design pattern directly from the requirements. The request is then captured in terms of a well-known design pattern. The design becomes rigid and unable to answer to changes in requirements. In this course on design patterns, students are actively pursued to not apply design patterns up-front. Design patterns come the other way around. Once a tailored solution is designed, parts of the design start exhibiting behavior which is a known hallmark of a certain design pattern. Only then do we change the design to accommodate the design pattern, and only because we have discovered the pattern in actual design. The key point is that a design pattern comes last to the design. Always with a relief; sometimes with a huge surprise in the form of a breakthrough.

The Right Time to Apply a Design Pattern
Introduction
Implementing the Observer
Supporting Different Notifications
Evolving the Observer
Design Patterns Backed by .NET Framework
When Is the Right Time to Apply a Design Pattern?
Summary
Cascading Factories to Eliminate Dependencies
Vacation Builder Example
Pulling the Abstract Factory Out
Using Inversion of Control to Resolve Dependencies
Cascading Factories Explained
Abstract and Concrete Factories
Summary
Real World Composition Pitfalls
Introduction to Composite Design Pattern
Evolving the Graphic Elements Example
Discussing the Detailed Model
Abstraction vs. Implementation
Summary
Compositing the Control Role
Approaching the Problem
Refactoring the Initial Solution
Simplifying the Composite Element
Capitalizing on the Refactoring
Revisiting the Evolution of Composite
Command-query Separation and Composite
Summary
Object Composition Using Chain of Responsibility
Introducing Chain of Responsibility
Problem Statement
Initial Solution
Object Composition Instead of Class Inheritance
Implementing the Object Composition
Applying Chain of Responsibility
Chain of Responsibility Class Diagram
Compositing Objects at Run Time
Summary
Visitor Design Pattern and Encapsulation
Introduction to Visitor Design Pattern
Before the Visitor
Encapsulating the Model Data
The Usual Way of the Visitor
Preserving Encapsulation in the Visited Object
Preserving Encapsulation of Elements
Summary
Calling Protocols and the Visitor
A Word About Information Hiding
Calling Protocol on the Accept Method
Commanding Visitors vs. Querying Visitors
Implementing the Command Visitor
Accept Method as Coordinator
Summary
Using Mixin to Move Responsibilities Out
Introducing Mixins
Basic Example
Moving Responsibility to the Mixin
Mixin with Abstract Factories
Mixing Responsibilities into Unrelated Classes
Polymorphic Behavior of Mixins
Summary

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