The Decorator Pattern In Go

The final product is oddly satisfying.



T

he Decorator pattern is an incredibly useful and flexible technique to create forward-thinking code. It allows you to add functionality to an object dynamically at run time instead of compile time. What this means is that you don’t have to manually write new code to extend an object’s feature set, you can simply use the decorator pattern to add behavior as you need it!

It also solves the issue of becoming restricted by an extensive sub-class architecture. Instead of getting lost in inheritance, the Decorator pattern uses lots of smaller classes (in Go’s case structs) in order to wrap functionality around other objects. This way we can have many objects with variations of functionality instead of having to define each individual class.

We will split this article into three parts including the use cases, UML diagram, and implementation in Go for the Decorator pattern.

Use Cases

The Decorator pattern can be applied to a wide range of situations and scenarios. These include:

• A Shopping Cart — each item could be wrapped around a central customer order object in order to keep track of the total order price.
• Data Streaming — as you transfer data you may find out you want various combinations of encryption, compression, or formatting behavior depending on what the client wants.
• Legacy Code — if you have an object that you can’t change but need to extend its feature capability, you could do so with Decorator pattern.

UML Diagram

This pattern entails a pretty compact diagram. Starting from the top, the Component interface requires the method operation() to be implemented. This is done by both the ConcreteComponent and the Decorator objects themselves. Note the aggregation relationship between Component and Decorator meaning that a Component may have zero to many Decorators, but a Decorator cannot exist without a Component.

Essentially, we have a Component interface with its most basic form implemented by ConcreteComponent. Then the Decorator can be implemented by a ConcreteDecorator and wrapped around the ConcreteComponents.

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What's new in the go 1.15

Go announced Go 1.15 version on 11 Aug 2020. Highlighted updates and features include Substantial improvements to the Go linker, Improved allocation for small objects at high core counts, X.509 CommonName deprecation, GOPROXY supports skipping proxies that return errors, New embedded tzdata package, Several Core Library improvements and more.

As Go promise for maintaining backward compatibility. After upgrading to the latest Go 1.15 version, almost all existing Golang applications or programs continue to compile and run as older Golang version.

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Builder Design Pattern

What is Builder Design Pattern ? Why we should care about it ?

Starting from **Creational Design Pattern, **so wikipedia says “creational design pattern are design pattern that deals with object creation mechanism, trying to create objects in manner that is suitable to the situation”.

The basic form of object creations could result in design problems and result in complex design problems, so to overcome this problem Creational Design Pattern somehow allows you to create the object.

Builder is one of the** Creational Design Pattern**.

When to consider the Builder Design Pattern ?

Builder is useful when you need to do lot of things to build an Object. Let’s imagine DOM (Document Object Model), so if we need to create the DOM, We could have to do lot of things, appending plenty of nodes and attaching attributes to them. We could also imagine about the huge XML Object creation where we will have to do lot of work to create the Object. A Factory is used basically when we could create the entire object in one shot.

As **Joshua Bloch (**He led the Design of the many library Java Collections Framework and many more) – “Builder Pattern is good choice when designing the class whose constructor or static factories would have more than handful of parameters”

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Head First Design Patterns using Go — 3. Decorating Objects: The Decorator Pattern

A descriptive series on the design patterns based on the O’Reily book of the same name adapted to Go from Java

Table of Contents

0.  Introduction

1. Welcome to Design Patterns: the Strategy Pattern
2. Keeping your Objects in the know: the Observer Pattern
3. Decorating Objects: the Decorator Pattern
4. Baking with OO goodness: the Factory Pattern
5. Encapsulating Invocation: the Command Pattern
6. Being Adaptive: the Adapter and Facade Patterns
7. Encapsulating Algorithms: the Template Method Pattern
8. Well-managed Collections: the Iterator and Composite Patterns
9. The State of Things: the State Pattern
10. Controlling Object Access: the Proxy Pattern
11. Patterns of Patterns: Compound Patterns

This series of articles will run you by the design patterns the way it is explained in the Head First Design Patterns book using Go as the coding language.

Problem Statement 1:

• Welcome to Starbuzz Coffee.
• During initial days, they have limited set of offerings — HouseBlend, DarkRoast, Decaf, Espresso.
• Design a system to get the cost of the beverage ordered.

Solution:

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Go-patterns: Curated List Of Go Design Patterns, Recipes and Idioms

Go Patterns

A curated collection of idiomatic design & application patterns for Go language.

Creational Patterns

Pattern	Description	Status
Abstract Factory	Provides an interface for creating families of releated objects	✘
Builder	Builds a complex object using simple objects	✔
Factory Method	Defers instantiation of an object to a specialized function for creating instances	✔
Object Pool	Instantiates and maintains a group of objects instances of the same type	✔
Singleton	Restricts instantiation of a type to one object	✔

Structural Patterns

Pattern	Description	Status
Bridge	Decouples an interface from its implementation so that the two can vary independently	✘
Composite	Encapsulates and provides access to a number of different objects	✘
Decorator	Adds behavior to an object, statically or dynamically	✔
Facade	Uses one type as an API to a number of others	✘
Flyweight	Reuses existing instances of objects with similar/identical state to minimize resource usage	✘
Proxy	Provides a surrogate for an object to control it's actions	✔

Behavioral Patterns

Pattern	Description	Status
Chain of Responsibility	Avoids coupling a sender to receiver by giving more than object a chance to handle the request	✘
Command	Bundles a command and arguments to call later	✘
Mediator	Connects objects and acts as a proxy	✘
Memento	Generate an opaque token that can be used to go back to a previous state	✘
Observer	Provide a callback for notification of events/changes to data	✔
Registry	Keep track of all subclasses of a given class	✘
State	Encapsulates varying behavior for the same object based on its internal state	✘
Strategy	Enables an algorithm's behavior to be selected at runtime	✔
Template	Defines a skeleton class which defers some methods to subclasses	✘
Visitor	Separates an algorithm from an object on which it operates	✘

Synchronization Patterns

Pattern	Description	Status
Condition Variable	Provides a mechanism for threads to temporarily give up access in order to wait for some condition	✘
Lock/Mutex	Enforces mutual exclusion limit on a resource to gain exclusive access	✘
Monitor	Combination of mutex and condition variable patterns	✘
Read-Write Lock	Allows parallel read access, but only exclusive access on write operations to a resource	✘
Semaphore	Allows controlling access to a common resource	✔

Concurrency Patterns

Pattern	Description	Status
N-Barrier	Prevents a process from proceeding until all N processes reach to the barrier	✘
Bounded Parallelism	Completes large number of independent tasks with resource limits	✔
Broadcast	Transfers a message to all recipients simultaneously	✘
Coroutines	Subroutines that allow suspending and resuming execution at certain locations	✘
Generators	Yields a sequence of values one at a time	✔
Reactor	Demultiplexes service requests delivered concurrently to a service handler and dispatches them syncronously to the associated request handlers	✘
Parallelism	Completes large number of independent tasks	✔
Producer Consumer	Separates tasks from task executions	✘

Messaging Patterns

Pattern	Description	Status
Fan-In	Funnels tasks to a work sink (e.g. server)	✔
Fan-Out	Distributes tasks among workers (e.g. producer)	✔
Futures & Promises	Acts as a place-holder of a result that is initially unknown for synchronization purposes	✘
Publish/Subscribe	Passes information to a collection of recipients who subscribed to a topic	✔
Push & Pull	Distributes messages to multiple workers, arranged in a pipeline	✘

Stability Patterns

Pattern	Description	Status
Bulkheads	Enforces a principle of failure containment (i.e. prevents cascading failures)	✘
Circuit-Breaker	Stops the flow of the requests when requests are likely to fail	✔
Deadline	Allows clients to stop waiting for a response once the probability of response becomes low (e.g. after waiting 10 seconds for a page refresh)	✘
Fail-Fast	Checks the availability of required resources at the start of a request and fails if the requirements are not satisfied	✘
Handshaking	Asks a component if it can take any more load, if it can't, the request is declined	✘
Steady-State	For every service that accumulates a resource, some other service must recycle that resource	✘

Profiling Patterns

Pattern	Description	Status
Timing Functions	Wraps a function and logs the execution	✔

Idioms

Pattern	Description	Status
Functional Options	Allows creating clean APIs with sane defaults and idiomatic overrides	✔

Anti-Patterns

Pattern	Description	Status
Cascading Failures	A failure in a system of interconnected parts in which the failure of a part causes a domino effect	✘

Download Details:

Author: tmrts
Source Code: https://github.com/tmrts/go-patterns 
License: Apache-2.0 license

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Design Patterns — Decorator Design Pattern

Introduction

The decorator design pattern is a software design pattern that helps you add responsibilities to an object at runtime. This pattern is considered to be a structural design pattern. This type of pattern focuses on the relationships between classes and how they can help solve specific problems.

The Gang of Four, in their book Design Patterns: Elements of Reusable Object-Oriented Software, defined the intent of decorator pattern like this:

Intent:_ Attach additional responsibilities to an object dynamically. Decorators provide a flexible alternative to subclassing for extending functionality._

One of the key characteristics of this design pattern is that it follows the Single Responsibility Principle (SRP). This is because each “decoration” you add to an object, will be encapsulated within a class. This class’s responsibility will be to handle everything related to adding that decoration to that object.

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Time to assemble a 🍔

For purposes of learning the decorator pattern, let’s assume you want to create an object of type Hamburger.

How a hamburger is assembled varies. According to Burger King, there are 221,184 possible ways to order a Whopper. It will take you at least 200 years to eat these many hamburgers if you were to eat one hamburger for breakfast, lunch, and dinner! The possibilities are endless.

In a world without the decorator pattern, an approach you might take is to create a parent Hamburger class and then subclasses for the different types of hamburgers. This could easily become a maintenance headache as it will make troubleshooting more difficult due to the complexity of multiple levels of inheritance.

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