# Adding variables to a binding

**URL:** <https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618>\
**Category:** Ruby\
**Created:** [February 11, 2006, 11:12pm UTC](https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618 "2006-02-11T23:12:38Z")\
**Posts on this page:** 4\
**Page:** 1

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**Author:** ![marcus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/85e7bf/32.png) [@marcus](https://www.ruby-forum.com/u/marcus)\
**Post date:** [February 11, 2006, 11:12pm UTC](https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618/1 "2006-02-11T23:12:38Z")

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I need to run an ERB template (a normal Rails view template) in a Rails  
model (and then write the result to a file). The problem is that I need  
to run it in the scope of the calling controller. So I was thinking of  
creating a binding in the controller and pass into the model and use the  
binding there. I do however need to add variables from the model scope  
into the binding. How do I do this? Thought of using eval with the  
binding but it only seems to take an input string to eval (a block would  
have been nice I think).

The reason I do this is that the model in question is a STI model and  
each sub class may need to add different variables. If you can think of  
a better way to accomplish what I want I’ll be glad to hear 🙂

Thanks,

/Marcus

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**Author:** ![marcus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/85e7bf/32.png) [@marcus](https://www.ruby-forum.com/u/marcus)\
**Post date:** [February 11, 2006, 11:46pm UTC](https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618/2 "2006-02-11T23:46:28Z")

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On 2/11/06, marcus [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote:

> each sub class may need to add different variables. If you can think of  
> a better way to accomplish what I want I’ll be glad to hear 🙂

If I understand correctly, you want something like this:

def outerscope  
innerscope(binding)  
p foo,bar,baz #problematic  
end

def innerscope(bdg)  
eval “foo=bar=baz=1”, binding  
end

This works, sort of. Unfortunately, ruby’s local variables are  
lexically scoped, which means that once you get back to outerscope,  
foo, bar, and baz (which _are_ now in outerscope’s binding) won’t be  
recognized as local variables. (Unless you use eval again to get at  
them…) For most purposes, they are unusable.

How about this instead:

def outerscope  
vars={}  
innerscope(vars)  
p vars[:foo],vars[:bar],vars[:baz]  
end

def innerscope(vars)  
vars[:foo]=vars[:bar]=vars[:baz]=1  
end

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<div class="post-metadata">

**Author:** ![marcus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/85e7bf/32.png) [@marcus](https://www.ruby-forum.com/u/marcus)\
**Post date:** [February 11, 2006, 11:57pm UTC](https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618/3 "2006-02-11T23:57:52Z")

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Caleb C. skrev:

> def innerscope(vars)  
> vars[:foo]=vars[:bar]=vars[:baz]=1  
> end

The problem is that ERB#result(binding) takes a binding so I need the  
binding. The templates used in this case relies on Rails rules (member  
variables in a controller are available in the ERB template) and I need  
to create a binding containing everything from the controller scope (and  
then add the new needed stuff from the model).

What about passing a block from outer scope and call it from inner scope  
and pass in a Hash with variables from the inner scope, then loop over  
the variables and add those as instance members (using instance\_eval),  
create the binding (inside the block) and then invoke ERB.result. Could  
that work?

/Marcus

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<div class="post-metadata">

**Author:** ![marcus](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/m/85e7bf/32.png) [@marcus](https://www.ruby-forum.com/u/marcus)\
**Post date:** [February 12, 2006, 4:33am UTC](https://www.ruby-forum.com/t/adding-variables-to-a-binding/53618/4 "2006-02-12T04:33:17Z")

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DÅ?a Sobota 11 Február 2006 23:12 marcus napísal:

> each sub class may need to add different variables. If you can think of  
> a better way to accomplish what I want I’ll be glad to hear 🙂
> 
> Thanks,
> 
> /Marcus

I -think- instance variables get exported from the ERB template into the  
calling method.

David V.