# Meta Programming Question **URL:** \ **Category:** Ruby\ **Created:** [March 5, 2008, 8:55am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021 "2008-03-05T08:55:50Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 5, 2008, 8:55am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/1 "2008-03-05T08:55:50Z")
Hello! Consider this case: myHash = {:a\_line\_of\_code =\> “pre\_count = Posts.count”, :another\_line =\> %q~message = get\_formatted\_message(#{pre\_count})~} If I have a hash like this which contains code snippets as strings, How can I execute them? Moreover consider also that the second code snippet uses the value of the variable assigned in the first one. Regards, Mohsin ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 5, 2008, 9:21am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/2 "2008-03-05T09:21:13Z")
On Mar 5, 1:51 am, MohsinHijazee [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > snippet uses the value of the variable assigned in the first one. > > Regards, > Mohsin If you need to use a variable from a hash maybe you should be using it outside the hash context. What I mean is that probably you shouldn’t be putting a variable there. You can always use eval to execute strings, but may not be a great idea. In any case, you may use procs instead of storing variables if what you want is dynamically generated values for the hash. > > hash = {:something =\> proc{ Posts.count }, :other\_thing =\> proc{|var| do\_something\_with(var)}} and you could call > > hash[:other\_thing][hash[:something]] but the ugliness of that cries desperately for a more elegant way. If you need to execute code, I think there is a feature or Ruby called errr, methods. Could you give more details of what you are trying? ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 5, 2008, 11:35am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/3 "2008-03-05T11:35:46Z")
On Mar 5, 1:19 pm, Rubén Medellín [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > If I have a hash like this which contains code snippets as strings, > > idea. > > but the ugliness of that cries desperately for a more elegant way. If > > you need to execute code, I think there is a feature or Ruby called > > errr, methods. > > Could you give more details of what you are trying? I am actually trying to automat the testing of an existing Rails application to the point where I only specify that what function to be tested with what params and what to expect in the response. Some of the functions being tested change the state of the system that’s why its necessary to calcuate some of the system stats before executing the test call to that function and after the test call and then to check the before and after responses to validate that the call really made the change to the system. Here is the structure (yet rough) to list all the tests in the system which would be automatically executed. # This is hash and it would be iterated mytests = { :test\_delete\_with\_wrong\_id =\> { :method =\> :get # This before would be executed befoer calling the above mention method :before =\> “json = Customer.find(1).to\_json” :url =\> [‘/databases/:database\_id/entities/:id.format’, 34, 56] :after \>= “json = @response.body” :params =\> {} :session =\> {‘user’ =\> user} # Response should be succuss :response =\> :success # Each of the assertions in this array would be executed :assertions =\> [“assert json, json”] } } ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 5, 2008, 4:52pm UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/4 "2008-03-05T16:52:14Z")
On Wed, Mar 5, 2008 at 2:35 AM, MohsinHijazee [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > get\_formatted\_message(#{pre\_count})~} > > > be putting a variable there. > > > > > > > hash[:other\_thing][hash[:something]] > > > > what > > > > list all the tests in the system which would be automatically > > > > executed. Is there a reason that Test::Unit (with appropriate setup and teardown for the test cases) won’t work? If it does, that would be better than reinventing the wheel. If it doesn’t, knowing what limitation you hit with that might help people propose an appropriate solution. ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 6, 2008, 1:35am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/5 "2008-03-06T01:35:22Z")
If you are testing and want to verify that a method has been called with the appropriate parameters, check out a library like FlexMock ([http://onestepback.org/software/flexmock/](http://onestepback.org/software/flexmock/)) ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 7, 2008, 8:38am UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/6 "2008-03-07T08:38:04Z")
2008/3/5, MohsinHijazee [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > If I have a hash like this which contains code snippets as strings, > How can I execute them? Moreover consider also that the second code > snippet uses the value of the variable assigned in the first one. Mohsin, as others have mentioned you should probably use other libraries, but just in case you want to continue to eval strings, there’s no problem with assigning variables and using them later: irb(main):001:0\> eval “var = 123” =\> 123 irb(main):002:0\> eval “2 \* var” =\> 246 irb(main):003:0\> Regards, Pit ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 7, 2008, 4:11pm UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/7 "2008-03-07T16:11:28Z")
On Fri, Mar 7, 2008 at 8:37 AM, Pit C. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > irb(main):001:0\> eval “var = 123” > =\> 123 > irb(main):002:0\> eval “2 \* var” > =\> 246 > irb(main):003:0\> > > Regards, > Pit This does not really serve a lot as var is visible in the eval binding _only_. E.g. puts var # will not output 123, not even 42 😉 Cheers Robert – [http://ruby-smalltalk.blogspot.com/](http://ruby-smalltalk.blogspot.com/) * * * Whereof one cannot speak, thereof one must be silent. Ludwig Wittgenstein ---
**Author:** ![MohsinHijazee](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/e68b1a/32.png) [@MohsinHijazee](https://www.ruby-forum.com/u/MohsinHijazee)\ **Post date:** [March 7, 2008, 4:34pm UTC](https://www.ruby-forum.com/t/meta-programming-question/131021/8 "2008-03-07T16:34:08Z")
2008/3/7, Robert D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > This does not really serve a lot as var is visible in the eval binding _only_. Where have you got the requirement from, that those variables should be visible outside of the eval code? Regards, Pit