# Code Smell 292 - Missing Return > TL;DR: Missing return statements cause unexpected behavior. # Problems πŸ˜” - Silent failures - Unreliable results - Hard debugging - Inconsistent and misleading behavior - Broken logic # Solutions πŸ˜ƒ 1. Always return values 2. Use clear flow 3. Validate conditions 4. Test all return paths 5. Use [early returns](https://maximilianocontieri.com/code-smell-156-implicit-else) 6. Remove [IFs](https://maximilianocontieri.com/refactoring-014-remove-if) # Refactorings βš™οΈ %[https://maximilianocontieri.com/refactoring-014-remove-if] # Context πŸ’¬ When you forget to return a value, your function keeps executing and your app might show incomplete or wrong information. # Sample Code πŸ“– ## Wrong ❌ ```kotlin fun totalDistance(activity: Activity): Double { if (activity.type == "Running") { activity.calculateDistance() // Missing return here } else { return 0.0 } // Other options are omitted for simplicity // Some languages raise a runtime error // If the function does not return a value // of the correct type (in this case a Double) } ``` ## Right πŸ‘‰ ```kotlin fun totalDistance(activity: Activity): Double { if (activity.type == "Running") { return activity.calculateDistance() // Now it returns the value } else { return 0.0 } } ``` # Detection πŸ” [X] Automatic You can detect this smell when your function lacks a return statement in certain branches. Most static analyzers and linters often catch this. # Tags 🏷️ - IFs # Level πŸ”‹ [x] Beginner # Why the Bijection Is Important πŸ—ΊοΈ it's important to maintain a clear and predictable relationship between your code and the [Real World](https://maximilianocontieri.com/the-one-and-only-software-design-principle). If a function is intended to calculate and return a value, it should always do so. Failing to return a value breaks the [MAPPER](https://maximilianocontieri.com/what-is-wrong-with-software), leading to inaccurate behavior and unreliable results. # AI Generation πŸ€– AI tools usually don't generate this smell. # AI Detection πŸ₯ƒ Most AI-powered linters quickly catch missing returns with static analysis or by examining your code's [Abstract Syntax Tree](https://en.wikipedia.org/wiki/Abstract_syntax_tree). ## Try Them! πŸ›  *Remember: AI Assistants make lots of mistakes* | Without Proper Instructions | With Specific Instructions | | -------- | ------- | | [ChatGPT](https://chat.openai.com/?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [ChatGPT](https://chat.openai.com/?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [Claude](https://claude.ai/new?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [Claude](https://claude.ai/new?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [Perplexity](https://www.perplexity.ai/?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [Perplexity](https://www.perplexity.ai/?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [Copilot](https://www.bing.com/chat?showconv=1&sendquery=1&q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [Copilot](https://www.bing.com/chat?showconv=1&sendquery=1&q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [Gemini](https://gemini.google.com/?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [Gemini](https://gemini.google.com/?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [DeepSeek](https://chat.deepseek.com/?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [DeepSeek](https://chat.deepseek.com/?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | | [Meta AI](https://www.meta.ai/chat?q=Correct+and+explain+this+code%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | [Meta AI](https://www.meta.ai/?q=correct+the+missing+return%3A+%60%60%60kotlin%0D%0Afun+totalDistance%28activity%3A+Activity%29%3A+Double+%7B%0D%0A++++if+%28activity.type+%3D%3D+%22Running%22%29+%7B%0D%0A++++++++activity.calculateDistance%28%29+%0D%0A++++++++%2F%2F+Missing+return+here%0D%0A++++%7D+else+%7B%0D%0A++++++++return+0.0%0D%0A++++%7D%0D%0A++++%2F%2F+Other+options+are+omitted+for+simplicity%0D%0A++++%2F%2F+Some+languages+raise+a+runtime+error+%0D%0A++++%2F%2F+If+the+function+does+not+return+a+value%0D%0A++++%2F%2F+of+the+correct+type+%28in+this+case+a+Double%29%0D%0A%7D%0D%0A%60%60%60) | # Conclusion 🏁 A missing return statement breaks your code’s flow and produces unreliable results. Always ensure every branch in your function returns something meaningful. # Relations πŸ‘©β€β€οΈβ€πŸ’‹β€πŸ‘¨ %[https://maximilianocontieri.com/code-smell-73-exceptions-for-expected-cases] %[https://maximilianocontieri.com/code-smell-102-arrow-code] %[https://maximilianocontieri.com/code-smell-115-return-true] %[https://maximilianocontieri.com/code-smell-118-return-false] %[https://maximilianocontieri.com/code-smell-186-hardcoded-business-conditions] %[https://maximilianocontieri.com/code-smell-36-switchcaseelseifelseif-statements] %[https://maximilianocontieri.com/code-smell-156-implicit-else] # Disclaimer πŸ“˜ Code Smells are my [opinion](https://maximilianocontieri.com/i-wrote-more-than-90-articles-on-2021-here-is-what-i-learned). # Credits πŸ™ Photo by [Tim Johnson](https://unsplash.com/@mangofantasy) on [Unsplash](https://unsplash.com/photos/white-and-gray-animal-on-gray-rocky-mountain-during-daytime-ywIZ8ZYxzWU) * * * > A bug is never just a mistake. It represents something bigger. _Sergey Zefirov_ %[https://maximilianocontieri.com/software-engineering-great-quotes] * * * This article is part of the CodeSmell Series. %[https://maximilianocontieri.com/how-to-find-the-stinky-parts-of-your-code]