class_eval and open classes

Question

I am using Spree, and Spree has a class called Order that looks like:

module Spree
  class Order
    # class definition.
  end
end

In my own app, I have been customising Order like so:

Spree::Order.class_eval do
  # customisations
end

My question is, can I simply just do this:

module Spree
  class Order
    # My own customisations.
  end
end

Any downsides to this? Essentially, I want to avoid using class_eval.

hey.. did you find a solution to this? I'm now just getting started with spree, and need to add a constant to the Spree::Order class. using `class_eval` somehow isn't working for constants, and without class_eval, I can't figure out how to access other methods in the class that I am reopening. — kapad, Jul 17 '18 at 09:36
Try using `@@some_constant`. Not a Spree issue, but a general Ruby weirdness. — Benjamin Tan Wei Hao, Jul 18 '18 at 08:34
yep.. that's what I did and it worked. One note though, I had to `require` the module/class that I was opening prior to opening it. This ensured that the original class file was loaded before I opened it again to change it to avoid getting class not found errors. — kapad, Jul 18 '18 at 10:16

score 6 · Accepted Answer · edited Jun 21 '19 at 06:23

6

Benjamin, reopen class will not inform you (but class_eval will raise error) if the existing class does not exist or not loaded.

But if you have test coverage, reopen class should be safe I guess?

See https://stackoverflow.com/a/900508/474597 for more detailed explanation.

edited Jun 21 '19 at 06:23

lulalala

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answered Mar 10 '14 at 02:52

Huiming Teo

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Ah good point. I'm in the process of _existing_ `class_eval`ed classes. – Benjamin Tan Wei Hao Mar 10 '14 at 02:59

score 0 · Answer 2 · answered Mar 11 '14 at 17:08

0

you cant alter the class without class_eval. just try to override one method, and all other methods are gone. with class_eval you avoid it. thats the ruby way.

answered Mar 11 '14 at 17:08

Tim Kretschmer

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@raj englighten me! – Tim Kretschmer Feb 09 '18 at 07:52
How does opening a class and over riding a method remove all other methods? Can you show an example? – raj Feb 09 '18 at 14:42
maybe you're right. can't remember. might be rails specfic. in rails you need to use class_eval, otherwise the initial class evaportaes. – Tim Kretschmer Feb 12 '18 at 06:13
The initial class would never evaporate if you reopen a class in rails. Can you show me any example resource ? I couldnt find any. – raj Feb 12 '18 at 15:46
i don't need any resource. that's just how rails is working. might has to do with its internal cache_classes ? – Tim Kretschmer Feb 20 '18 at 06:56

class_eval and open classes

2 Answers2