How can I extend a ruby class from a class defined in a module?

Question

I have the following files:

file.rb

require_relative 'foo/bar'
baz = Foo::Stuff::Baz.new
# do stuff

foo/bar.rb

require_relative 'stuff/baz'
module Foo
    class Bar
        def initialize
            # do stuff
        end
    end
end

foo/stuff/baz.rb

module Foo
    module Stuff
        class Baz < Bar
        end
    end
end

I get the following error:

`': uninitialized constant Foo::Stuff::Bar (NameError)

Is there something I'm doing wrong here? Is this even possible in Ruby? In case it matters, I'm only doing this because I need to inherit the initialize method specifically.

Eric Duminil · Accepted Answer · 2017-01-05 23:13:05Z

3

It works just fine when you put them in the same script :

module Foo
  class Bar
    def initialize
      # do stuff
    end
  end
end

module Foo
  module Stuff
    class Baz < Bar
    end
  end
end

p Foo::Stuff::Baz.ancestors
#=> [Foo::Stuff::Baz, Foo::Bar, Object, Kernel, BasicObject]

So it must be a problem with the way or order in which you require your files.

Also, if you just need just one specific method from Foo::Bar in Foo::Stuff::Baz, you could put this method in a module, and include this module in both classes.

answered Jan 5, 2017 at 23:13

Eric Duminil

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1 Comment

sluther Over a year ago

Yep, you were right. The problem was that I require foo/stuff/baz.rb in foo/bar.rb. I'm marking your answer as the correct one.

knut · Accepted Answer · 2017-01-05 23:26:44Z

3

Your foo/stuff/baz.rb does not contain any require statement and you tell nothing about a main programm. So I think you just don't load the code.

Ruby has no automatic loading depending on folder path, you must explicitly load the source code. In your case you need a require_relative '../bar' in the file foo/stuff/baz.rb. Then the class Foo::Bar is known:

require_relative '../bar'

module Foo
    module Stuff
        class Baz < Bar
        end
    end
  end

  p Foo::Stuff::Baz.new
  p Foo::Stuff::Baz.ancestors

The result:

#<Foo::Stuff::Baz:0x00000002ff3c30>
[Foo::Stuff::Baz, Foo::Bar, Object, Kernel, BasicObject]

The initialize-method of Foo::Bar is executed.

A more realistic architecture would be the usage of a main file where you load all code files, e.g.:

foo.rb
foo/bar.rb
foo/stuff/baz.rb

and foo.rb would contain:

require_relative 'foo/bar'
require_relative 'foo/stuff/baz'

edited Jan 5, 2017 at 23:26

answered Jan 5, 2017 at 23:05

knut

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3 Comments

sluther Over a year ago

I do have the require_relative statements in there, actually. I should have included them in my post.

sluther Over a year ago

So, if I'm not mistaken, I should have the require_relatives for everything in the main file. I'll give that a shot instead.

sluther Over a year ago

Thanks, I figured it out. I realized that the problem is the require statement in my foo/bar.rb file.

Eric Platon · Accepted Answer · 2017-01-05 22:52:32Z

1

Foo::Bar is defined. You can also access ::Foo::Bar ("root" module) when there are issues finding the right namespace.

edited Jan 5, 2017 at 22:52

answered Jan 5, 2017 at 22:46

Eric Platon

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Comments

MVP · Accepted Answer · 2017-01-13 10:35:32Z

0

It does not work because in baz.rb namespace there is no any reference to the Bar class; should simply enter:

class Bar; end

So the baz.rb structure becomes simply have: (foo/stuff/baz.rb)

module Foo
  class Bar; end
  module Stuff
    class Baz < Bar
    end
  end
end

answered Jan 13, 2017 at 10:35

MVP

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