Question

I have the following code, meant to turn a normal variable into an instance variable.

BasicObject.class_eval do
    def instance(ins)
        self.instance_variable_set("@#{ins}", ins)
    end
end

Lets say the user says

class X
  foo = 3
end
bar = X.new
bar.instance(:foo)

What I want it to do is set the new created variable, @foo to 3, instead, it sets @foo to :foo. How do I make the code do what I want?

Answer 1

Inside your instance method, the parameter ins contains the name of the variable, not its value. As written, there’s no way to get at its value from that point.

If you call instance from a point in the code where the source variable is actually visible, which it’s not in your example (see my comment above), you can also pass the local variable binding, and then use that. Something like this:

def instance(var, bound)
    eval "@#{var}=#{var}", bound
end

Which would work like this:

foo = 3
instance('foo', binding)
@foo   # => 3