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Editorial Team
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Asked: 2026-06-10T19:13:13+00:00

I just discovered Ruby’s metaprogramming (after 7 years of using Ruby, it was about

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I just discovered Ruby’s metaprogramming (after 7 years of using Ruby, it was about time!) and I have this question:

Assuming I run a program that uses class_eval and other metaporgramming functions to add methods to a class, is there an easy way, when re-running the same program, to have these new methods already defined, or do I have to program my own system which, every time class_eval is used, also save the generated code in a file in order to re-evaluate it the next time I run the program?

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  1. Editorial Team

    This is not how it’s done. A proper way is, when you run the program next time, to run all those calls to define_method, class_eval (and whatnot) again and define methods in run-time.

    Imagine what would happen if generated methods persisted in your source code? Would you like your attr_accessor to replace itself with two new methods?

    What if you’re writing such a meta-method yourself and you change it. How do you think all those saved generated methods will be updated?

    I don’t know where you read about metaprogramming, but I strongly recommend this book: Metaprogramming Ruby. It should clear your head. 🙂

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