Question

I am trying to set a local variable to an existing binding

def foo_callback
  lambda { |name| p name }
end
b = foo_callback.binding

The binding doesn’t have any local variables to begin with:

b.eval("local_variables") # => []

Let us set a primitive local variable to the binding:

b.eval("age=30")

Everything works as expected:

b.eval("local_variables") # => ["age"]
b.eval("age") # => 30

Now, let us try to set a non-primitive local variable to the binding:

country = Country.first
b.eval("lambda {|v| country = v}").call(country)

Note: The technique for setting the variable is borrowed from the facet gem. I tried the ruby 1.9 safe implementation with same results.

The binding does not reflect the local variable country.

b.eval("local_variables") # => ["age"]

How do I get around this issue? Essentially, I want to declare a new variable in a binding using the value of an existing, non primitive variable.

I am on Ruby 1.8.7.

Answer 1

You’re creating country outside of the binding, and then the country inside the lambda is only valid within that scope. Why not eval it if you need to inject that into the binding as well?

Update

Try declaring the variable outside of the scope of the lambda but inside the scope of the binding:

 b.eval("country = nil; lambda {|v| country = v}").call(country)