Meta Programming Question

Ruby
1

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

2

On Mar 5, 1:51 am, MohsinHijazee [email protected] 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?

3

On Mar 5, 1:19 pm, Rubén Medellín [email protected] 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”]
}

}

4

On Wed, Mar 5, 2008 at 2:35 AM, MohsinHijazee [email protected]
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.

5

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/)

6

2008/3/5, MohsinHijazee [email protected]:

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

7

On Fri, Mar 7, 2008 at 8:37 AM, Pit C. [email protected]
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 :wink:

Cheers
Robert

–
http://ruby-smalltalk.blogspot.com/

Whereof one cannot speak, thereof one must be silent.
Ludwig Wittgenstein

8

2008/3/7, Robert D. [email protected]:

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