Global variables create tight coupling between different parts of your Rails application, making your code harder to maintain and test.
When you use global variables, you create hidden dependencies that are not obvious from looking at a class or method signature. This makes it
difficult to understand what data a piece of code depends on, and it becomes nearly impossible to test components in isolation.
Global variables also introduce the risk of unexpected side effects. Since they can be modified from anywhere in your application, tracking down
bugs becomes much more challenging. In a multi-threaded environment like Rails, global variables can also lead to race conditions.
Rails provides better alternatives for sharing data across your application. These alternatives are more explicit, easier to test, and follow Rails
conventions.
What is the potential impact?
Using global variables can lead to:
- Code that is difficult to test and debug
- Tight coupling between unrelated parts of your application
- Unexpected side effects and hard-to-track bugs
- Race conditions in multi-threaded environments
- Violation of Rails conventions and best practices
