Using Boolean variables as flags introduces accidental implementation complexity and pollutes the code with Ifs. Using Boolean variables as flags introduces accidental implementation complexity and pollutes the code with Ifs. TL;DR: avoid Boolean variables, they lead to conditional logic and force you to write Ifs. Create polymorphic states instead. TL;DR: avoid Boolean variables, they lead to conditional logic and force you to write Ifs. Create polymorphic states instead. Problems 😔 Extensibility
Comparison in some languages
Missed polymorphism
Limited semantics
Primitive obsession Extensibility Comparison in some languages Missed polymorphism polymorphism Limited semantics Primitive obsession Solutions 😃 If Boolean maps to a real-world entity is safe.
Model Booleans as a State to favor Extensibility following the Open/Closed Principle.
Create intention-revealing objects
Replace Booleans with polymorphism If Boolean maps to a real-world entity is safe. Model Booleans as a State to favor Extensibility following the Open/Closed Principle. Open/Closed Principle Create intention-revealing objects Replace Booleans with polymorphism polymorphism Refactorings ⚙️ https://hackernoon.com/refactoring-014-how-to-remove-if?embedable=true https://hackernoon.com/refactoring-014-how-to-remove-if?embedable=true Examples 📚 Flags
Status indicators Flags Status indicators Context 💬 Boolean variables tempt you to oversimplify complex domains. When you use a Boolean, you force two states where many might exist. This creates coupling because you hardcode behavior based on true/false checks scattered throughout your code. true/false Booleans also hide intent. A variable named flag tells you nothing about what it represents in the real world. Even descriptive names like isActive or hasPermission leak implementation details instead of revealing domain concepts. isActive hasPermission The problems multiply when you need a third state. You cannot extend a Boolean without breaking existing code. You end up with multiple Boolean combinations that create implicit states, making your code fragile and hard to understand. Real-world entities rarely have just two states. A traffic light isn't "on" or "off"—it's red, yellow, or green. An order isn't just "paid" or "unpaid"—it might be pending, processed, shipped, or delivered. Sample Code 📖 Wrong 🚫 <?

function processBatch(
    bool $useLogin,
    bool $deleteEntries,
    bool $beforeToday) {
    // ...
} <?

function processBatch(
    bool $useLogin,
    bool $deleteEntries,
    bool $beforeToday) {
    // ...
} Right 👉 <?

function processBatch(
    LoginStrategy $login,
    DeletionPolicy $deletionPolicy,
    Date $cutoffDate) {
    // ...
} <?

function processBatch(
    LoginStrategy $login,
    DeletionPolicy $deletionPolicy,
    Date $cutoffDate) {
    // ...
} Detection 🔍 Manual Manual Automatic detection can warn for B usage, but this can yield false positives. You can search for boolean attributes in classes, Boolean parameters in methods, and conditional statements that check Boolean values. Look for variables with "is", "has", "can", or "flag" in their names. Watch for multiple Boolean combinations that represent different states. Exceptions 🛑 Real-world true/false rules
Some languages have issues with Boolean comparators. Real-world true/false rules Some languages have issues with Boolean comparators. In these coupled with accidental complexity languages, Booleans are a common error source. Tags 🏷️ IFs IFs Level 🔋 [x ] Intermediate Why the Bijection Is Important 🗺️ Your code should always mirror reality. When you use a Boolean to represent an employee's status, you break the bijection between your software and the MAPPER. MAPPER Real employees don't have a true/false state. They have concrete statuses like "on vacation" or "working remotely." true/false This broken mapping creates a gap between how domain experts think and how your code works. Business people talk about "vacation status" or "remote work," not about "is_on_vacation equals true." mapping When you model with Booleans, you force translation between business language and code, increasing cognitive load and error potential. The bijection violation compounds when requirements change. Adding a new employee status means modifying all the boolean logic scattered across your codebase. bijection With proper domain modeling, you simply add a new status class. The broken mapping makes your code rigid where reality is flexible. AI Generation 🤖 AI code generators frequently create Boolean flags because they optimize for brevity and simplicity. They often suggest is_active or has_permission flags when generating boilerplate code. is_active has_permission You need to explicitly request domain modeling to avoid this pattern. AI Detection 🧲 AI tools can detect Boolean variables with medium accuracy when you provide context. You need to specify that you want domain-driven design and state pattern usage. Simple prompts might not catch the smell without explicit instructions to avoid Booleans. Try Them! 🛠 Remember: AI Assistants make lots of mistakes Remember: AI Assistants make lots of mistakes Suggested Prompt: correct=Replace Boolean variables with polymorphism Suggested Prompt: correct=Replace Boolean variables with polymorphism Without Proper Instructions

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Qwen Qwen Qwen Qwen Qwen Qwen Qwen Conclusion 🏁 Take extra care when declaring something Boolean. Flags are difficult to maintain and extend. Boolean Learn more about the domain. Try migrating to state design pattern. Use polymorphism instead of ifs/switch/cases. state design pattern Relations 👩‍❤️‍💋‍👨 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xi-sit35t1 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xi-sit35t1 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xiii https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-v-evj3zs9 https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxi https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxv https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxx?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-xxxx?embedable=true https://hackernoon.com/code-smell-270-boolean-apis?embedable=true https://hackernoon.com/code-smell-270-boolean-apis?embedable=true More Information 📕 https://martinfowler.com/bliki/FlagArgument.html?embedable=true https://martinfowler.com/bliki/FlagArgument.html?embedable=true Also Known as 🪪 Flag Abuser Flag Abuser Credits 🙏 Photo by Phil Hearing on Unsplash Phil Hearing Unsplash This article is part of the CodeSmell Series. https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd?embedable=true https://hackernoon.com/how-to-find-the-stinky-parts-of-your-code-part-i-xqz3evd?embedable=true

Code Smell 07 - Avoid Boolean Variables

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