The "Abstract Document" design pattern is a structural design pattern that aims to provide a consistent way to handle
hierarchical and tree-like data structures by defining a common interface for various document types.
The Abstract Document pattern enables handling additional, non-static properties. This pattern
uses concept of traits to enable type safety and separate properties of different classes into
set of interfaces.
Wrapper
Convert the interface of a class into another interface the clients expect. Adapter lets classes work together that
couldn't otherwise because of incompatible interfaces.
Real-world example
Consider that you have some pictures on your memory card and you need to transfer them to your computer. To transfer them, you need some kind of adapter that is compatible with your computer ports so that you can attach a memory card to your computer. In this case card reader is an adapter.
Another example would be the famous power adapter; a three-legged plug can't be connected to a two-pronged outlet, it needs to use a power adapter that makes it compatible with the two-pronged outlets.
Yet another example would be a translator translating words spoken by one person to another
Provide a helper service instance on a client and offload common functionality away from a shared resource.
Real world example
A remote service has many clients accessing a function it provides. The service is a legacy application and is
impossible to update. Large numbers of requests from users are causing connectivity issues. New rules for request
frequency should be implemented along with latency checks and client-side logging.
Handle/Body
Decouple an abstraction from its implementation so that the two can vary independently.
Real-world example
Consider you have a weapon with different enchantments, and you are supposed to allow mixing
different weapons with different enchantments. What would you do? Create multiple copies of each
of the weapons for each of the enchantments or would you just create separate enchantment and set
it for the weapon as needed? Bridge pattern allows you to do the second.
The Business Delegate pattern adds an abstraction layer between
presentation and business tiers. By using the pattern we gain loose coupling
between the tiers and encapsulate knowledge about how to locate, connect to,
and interact with the business objects that make up the application.
Compose objects into tree structures to represent part-whole hierarchies. Composite lets clients
treat individual objects and compositions of objects uniformly.
Real-world example
Every sentence is composed of words which are in turn composed of characters. Each of these
objects are printable and they can have something printed before or after them like sentence
always ends with full stop and word always has space before it.
It is used to model, represent, and manage a set of persistent objects that are interrelated, rather than representing them as individual fine-grained entities.
Real world example
For a console, there may be many interfaces that need to be managed and controlled. Using the composite entity pattern, dependent objects such as messages and signals can be combined together and controlled using a single object.
Composite View
The purpose of the Composite View Pattern is to increase re-usability and flexibility when creating views for websites/webapps.
This pattern seeks to decouple the content of the page from its layout, allowing changes to be made to either the content
or layout of the page without impacting the other. This pattern also allows content to be easily reused across different views easily.
Wrapper
Attach additional responsibilities to an object dynamically. Decorators provide a flexible
alternative to subclassing for extending functionality.
Real-world example
There is an angry troll living in the nearby hills. Usually, it goes bare-handed but sometimes it
has a weapon. To arm the troll it's not necessary to create a new troll but to decorate it
dynamically with a suitable weapon.
Proxy Pattern
It is a technique where an object expresses certain behavior to the outside but in
reality delegates responsibility for implementing that behaviour to an associated object.
Real-world example
Imagine that we have adventurers who fight monsters with different weapons depending on their
abilities and skills. We must be able to equip them with different ones without having to
modify their source code for each one. The delegation pattern makes it possible by delegating
the dynamic work to a specific object implementing an interface with relevant methods.
