Question

I’ve created a ruby C extension TestExt, successfully compiled it, but when I try and use it in irb I can only access it’s methods after i’ve called include TestExt.

I’m testing it like this:

c:/test>irb -I lib
irb(main):001:0> require 'TestExt'
=> true
irb(main):002:0> TestExt.hello()
NoMethodError: undefined method `hello' for TestExt:Module
        from (irb):2
        from C:/Ruby192/bin/irb:12:in `<main>'
irb(main):003:0> TestExt.instance_methods
=> [:hello]
irb(main):004:0> include TestExt
=> Object
irb(main):005:0> TestExt.hello()
=> 0
irb(main):006:0> hello()
=> 0

Do you always have to include an extension? Is there an alternative way of includeing that doesn’t make the method hello global? Why can I see hello in the TestExt.instance_methods but not access it?

Answer 1

As you say yourself in your question, hello is an instance method, ergo you first need to mix your module into something, so that you have an instance to call it on.

When you include a mixin at the top-level, that is basically equivalent to

class Object
  include TestExt
end

which mixes TestExt into Object and thus makes hello available as an instance method of the Object class. Since everything inherits from Object, including Module, this makes the hello instance method available to both your TestExt module and the anonymous main object (which is what self evaluates to at the top-level).

Try ''.hello, and it will work also, since you mixed TestExt into Object and String inherits from Object.

Do you always have to include an extension?

No.

Is there an alternative way of includeing that doesn’t make the method hello global?

Yes: just don’t include it in the global scope.

Why can I see hello in the TestExt.instance_methods but not access it?

Because it’s an instance method.