Example

example.rb

class Greeter

  def greet(name)
    "Hello #{name}"
  end

end

class User

  def first_name
    "Foo"
  end

  def greet_with(&block)
    Greeter.new.instance_exec(&block)
  end

  def greet_first_name
    greet_with { greet(first_name) }
  end

end

User.new.greet_first_name

The problem here is that greet(first_name) is actually calling greet(self.first_name), and inside the instance_exec block, the self is no longer User. The block scope still sees local variables - it just can't run the method. So one solution is just putting the result of the method in a local var:

def greet_first_name
  name = first_name()
  greet_with { greet(name) }
end

instance_exec actually has a built-in pattern for this. It takes arguments which it will pass to the block. This is useful if you want to use methods or instance variables, without needing to put them into local variables. We just need to adjust the greet_with method a little:

  def greet_with(*args, &block)
    Greeter.new.instance_exec(*args, &block)
  end

  def greet_first_name
    greet_with(first_name) { |name| greet(name) }
  end

This way you can be more explicit about the original lexical scope you're using.
Neither is particularly pretty, but it's not a particularly common scenario either.

@shnikola Thank you