Скачать или смотреть Resolving undefined method Error in Ruby: Passing Functions Between Classes

Discover how to fix the `undefined method` error in Ruby when passing functions between classes without altering your code structure.
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This video is based on the question https://stackoverflow.com/q/68370458/ asked by the user 'Vision' ( https://stackoverflow.com/u/4518087/ ) and on the answer https://stackoverflow.com/a/68370684/ provided by the user 'Chris Heald' ( https://stackoverflow.com/u/271475/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Fixing the undefined method Error in Ruby

If you are a Ruby programmer, you may have encountered the frustrating undefined method error while attempting to pass functions between classes. This common issue often arises due to scope and method lookups. In this post, we'll explore an example that illustrates this problem and walk through a clear solution to get you back on track.

The Problem

Consider the following scenario:

You have two classes, Logger and Test. The Logger class records function calls along with their inputs and outputs, while the Test class contains a method named test_func that doubles its input.

Here’s a simplified version of the code:

[[See Video to Reveal this Text or Code Snippet]]

When you run this code, you encounter an error stating that test_func is an undefined method for the Logger class. This happens because the Logger class is trying to look up test_func within its own context rather than the context of the Test class.

The Solution

The solution to this problem involves ensuring that the Logger instance can correctly reference the test_func method defined within the instance of the Test class.

Revised Code Structure

We can modify the func_logger method in the Logger class to accept a method reference rather than a symbol. This allows us to call the method directly from the context of the Test class.

Here’s the corrected version of the relevant classes:

[[See Video to Reveal this Text or Code Snippet]]

Key Changes Explained

Pass Method Reference:

In the modified exec method of Test, instead of calling logger.func_logger(:test_func, input), we now use method(:test_func), which passes a Method object that is linked to the test_func defined in the instance context of the Test class.

Removed Symbol Lookup:

Since func_logger now directly calls the passed method reference, we don't need to perform any lookups via symbols, eliminating the source of the original error.

Conclusion

By passing a method reference from one class to another, you can avoid the undefined method error and maintain the structure of your code. This approach not only resolves the error but also adheres to good programming practices in Ruby.

If you find yourself stuck in a similar situation again, remember to check how methods are being referenced and the contexts they belong to. Happy coding!