How do I dynamically add an attr_reader

Question

I expect the following code to work as expected but it gives me a NoMethodError (private method `foo' called for #<MyClass...)

class MyClass
end

my_object = MyClass.new

my_object.instance_variable_set(:@foo, "bar")
MyClass.send("attr_reader", :foo)

puts my_object.foo

The problem is I'm using literally identical code in a larger application and it works exactly as I expect, but when I simplify it to this most basic example it fails.

(I understand there are many other ways to do what I'm doing in Ruby)

Answer 1

Use Module#class_eval:

By doing this, the block puts you in the context of MyClass, thus allowing you to call attr_reader

ruby-1.9.2-p136 :028 > my_object.instance_variable_set(:@foo, "bar")
 => "bar" 
ruby-1.9.2-p136 :029 > MyClass.class_eval{attr_reader :foo}
 => nil 
ruby-1.9.2-p136 :030 > my_object.foo
 => "bar"