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update SOLID
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‎notebooks/Untitled.ipynb

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{
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"cells": [
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"execution_count": null,
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"id": "f0da3cda",
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"outputs": [],
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"display_name": "Python 3 (ipykernel)",
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"language": "python",
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"name": "python",
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"nbformat": 4,
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"nbformat_minor": 5
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}

‎notebooks/WhenObjectsAreAlike.ipynb

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" print_dict(employee.to_dict())"
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]
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},
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{
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"cell_type": "markdown",
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"id": "9f680e25",
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"metadata": {},
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"source": [
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"## Inheritance Tax\n",
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"\n",
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"- \"You wanted a banana but what you got was a gorilla holding the banana and the entire jungle\" - Joe Armstrong\n",
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"- inheritance is a powerful tool but it can be misused\n",
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"- alternatives may be better to avoid the inheritance tax:\n",
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" - interfaces and protocols\n",
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" - delegation\n",
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" - mixins\n",
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"- interfaces and protocols give us polymorphism without inheritance\n",
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"- delegation is a way to use composition instead of inheritance\n",
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"- delegate to services - Has-A relationship Trumps Is-A relationship\n",
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"- use mixins to share code and functionality\n"
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]
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},
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{
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"cell_type": "markdown",
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"id": "80057b78",
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"metadata": {},
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"source": [
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"## SOLID principle\n",
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"\n",
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"- a popular software design principle using OOP\n",
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"- **inheritance** must follow L - Liskov Substitution principle\n",
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"\n",
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"### S: Single Responsibility Principle\n",
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"### S: Single Responsibility Principle (SRP)\n",
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"\n",
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"- a class should have one responsibility\n",
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"- one reason to change when the requirements change\n",
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"- \"one and only reason\" to change when the requirements change\n",
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"- a class should have a single, well-defined purpose; should be responsible for one aspect of the system's functionality\n",
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"\n",
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"#### How to Achieve the Single Responsibility Principle:\n",
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"\n",
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"- **Identify Responsibilities**:\n",
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" - carefully analyze the responsibilities of each class in your design\n",
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"\n",
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"- **Separate Concerns**: \n",
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" - if a class has multiple responsibilities, break it down into smaller classes, each with a single responsibility\n",
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" \n",
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"- **Use Cohesion**:\n",
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" - aim for high cohesion within classes, meaning that all the elements within a class should be related to its single responsibility\n",
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" \n",
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"- **Avoid God Objects**:\n",
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" - \"God objects\" are classes that try to do everything\n",
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" \n",
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"- **Refactor**: \n",
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" - if you find that a class is violating the SRP, refactor it to separate its responsibilities\n",
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" \n",
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"#### What does \"reason to change\" mean?\n",
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"\n",
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"- A \"reason to change\" refers to a specific actor or requirement that could cause the class to be modified; e.g.:\n",
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"\n",
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" - A class that handles both data persistence and user interface logic has two reasons to change: changes in the database schema and changes in the UI design.\n",
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" - A class that both calculates employee salary and generates reports has two reasons to change: changes in salary calculation rules and changes in report formatting.\n",
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"\n"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "5409782d",
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"metadata": {},
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"outputs": [],
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"source": [
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"# e.g. design violating SRP\n",
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"class Employee:\n",
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" def __init__(self, employee_id, name, salary):\n",
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" self.employee_id = employee_id\n",
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" self.name = name\n",
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" self.salary = salary\n",
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"\n",
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" def calculate_pay(self):\n",
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" # Calculate employee pay\n",
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" pass\n",
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"\n",
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" def generate_report(self):\n",
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" # Generate employee report\n",
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" pass\n",
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"\n",
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" def save_to_database(self):\n",
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" # Save employee data to database\n",
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" pass"
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]
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},
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{
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"cell_type": "code",
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"execution_count": null,
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"id": "f43f76ad",
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"metadata": {},
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"outputs": [],
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"source": [
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"# to adhere to SRP refactor the God class into three separate classes\n",
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"class Employee:\n",
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" def __init__(self, employee_id, name, salary):\n",
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" self.employee_id = employee_id\n",
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" self.name = name\n",
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" self.salary = salary\n",
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"\n",
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"class PayCalculator:\n",
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" def calculate_pay(self, employee):\n",
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" # Calculate employee pay\n",
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" pass\n",
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"\n",
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"class ReportGenerator:\n",
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" def generate_report(self, employee):\n",
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" # Generate employee report\n",
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" pass\n",
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"\n",
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"class EmployeeRepository:\n",
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" def save_to_database(self, employee):\n",
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" # Save employee data to database\n",
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" pass"
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]
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},
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{
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"cell_type": "markdown",
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"id": "259b858a",
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"metadata": {},
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"source": [
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"### O: Open/Closed\n",
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"- a class should be open to extension but closed to modification\n",
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"\n",
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"- \"Software entities (classes, modules, functions, etc.) should be open for extension, but closed for modification.\"\n",
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"- Open for Extension: \n",
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" - you should be able to add new functionality to your software without changing the existing code\n",
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"- Closed for Modification\n",
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" - once a piece of code is written and tested, you shouldn't need to modify its source code to accommodate new requirements\n",
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" \n",
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"#### Why is this important?\n",
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"\n",
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"- reduced risk of introducing bugs\n",
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" - modifying existing code can introduce unintended side effects and break working functionality\n",
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" - by extending instead of modifying, you minimize this risk\n",
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" \n",
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"- increased maintainability\n",
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" - code that adheres to the OCP is easier to maintain and adapt to changing requirements\n",
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"\n",
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"- improved reusability\n",
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" - well-designed, extensible code can be reused in different parts of your application or in other projects\n",
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" \n",
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"- enhanced stability\n",
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" - stable, unmodified code provides a reliable foundation for building new features\n",
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" \n",
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"#### How to Achieve the Open/Closed Principle:\n",
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"\n",
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"- common techniques for achieving the OCP include:\n",
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"\n",
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"- **Abstraction**: \n",
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" - using abstract classes or interfaces to define a contract that concrete classes must adhere to\n",
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" \n",
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"- **Inheritance**: \n",
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" - creating new classes that inherit from existing classes and override or extend their behavior\n",
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"\n",
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"- **Polymorphism**: \n",
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" - writing code that can work with objects of different types through a common interface\n",
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" \n",
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"- **Composition**: \n",
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" - building complex objects by combining simpler objects, rather than inheriting from them\n",
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" \n",
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"- **Design Patterns**: \n",
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" - using design patterns like the Strategy, Template Method, and Observer patterns, which are specifically designed to promote extensibility\n",
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" \n",
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"### L: Liskov Substitution\n",
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"\n",
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"- **inheritance** must follow L - Liskov Substitution principle\n",
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"- named after Barbara Liskov creator of CLU programming language\n",
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"- any subclass can be substituted for its superclass\n",
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" - any code that uses superclass can be replaced with it's subclass without breaking any code!\n",
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"- if two classes depend on each other, use a mixin class to reuse the dependence"
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]
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},
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{
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"cell_type": "markdown",
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"id": "9f680e25",
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"metadata": {},
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"source": [
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"## Inheritance Tax\n",
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"\n",
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"- \"You wanted a banana but what you got was a gorilla holding the banana and the entire jungle\" - Joe Armstrong\n",
1951-
"- inheritance is a powerful tool but it can be misused\n",
1952-
"- alternatives may be better to avoid the inheritance tax:\n",
1953-
" - interfaces and protocols\n",
1954-
" - delegation\n",
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" - mixins\n",
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"- interfaces and protocols give us polymorphism without inheritance\n",
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"- delegation is a way to use composition instead of inheritance\n",
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"- delegate to services - Has-A relationship Trumps Is-A relationship\n",
1959-
"- use mixins to share code and functionality\n"
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]
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},
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{
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"cell_type": "markdown",
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"id": "86ab0315",

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