Question

Let’s say we have two classes, Foo and Foo Sub, each in a different file, foo.rb and foo_sub.rb respectively.

foo.rb:

require 'foo_sub' class Foo     def foo         FooSub.SOME_CONSTANT     end end 

foo_sub.rb:

require 'foo' class FooSub < Foo     SOME_CONSTANT = 1 end 

This isn’t going to work due to the circular dependency – we can’t define either class without the other. There are various solutions that I’ve seen. Two of them I want to avoid – namely, putting them in the same file and removing the circular dependency. So, the only other solution I’ve found is a forward declaration:

foo.rb:

class Foo end require 'foo_sub' class Foo     def foo         FooSub.SOME_CONSTANT     end end 

foo_sub.rb

require 'foo' class FooSub < Foo     SOME_CONSTANT = 1 end 

Unfortunately, I can’t get the same thing to work if I have three files:

foo.rb:

class Foo end require 'foo_sub_sub' class Foo     def foo         FooSubSub.SOME_CONSTANT     end end 

foo_sub.rb:

require 'foo' class FooSub < Foo end 

foo_sub_sub.rb:

require 'foo_sub' class FooSubSub < FooSub     SOME_CONSTANT = 1 end 

If I require foo_sub.rb, then FooSub is an uninitialized constant in foo_sub_sub.rb. Any ideas how to get around this without putting them in the same file nor removing the circular dependency?

Answer 1

If you need to access a subclass from a superclass then there’s a good chance that your model is broken (i.e. it should be one class).

That said, there are a couple of obvious solutions:

1) just create a file that requires the foo files:

all_foos.rb:

require 'foo.rb' require 'foo_sub.rb' 

and remove the requires from foo.rb and foo_sub.rb.

2) remove the require from foo.rb

3) remove the require from foo_sub.rb and put the require in foo.rb after the class definition.

Ruby isn’t C++, it won’t complain about FooSub.SOME_CONSTANT until you call Foo#foo() 😉