From: Shadowfirebird <shadowfirebird@...>
Date: 2008-07-24T17:14:59+09:00
Subject: Re: circular 'require'

::slaps heel of hand to forehead::

The END{ require } thing isn't needed.  Setting $" solves the infinite
loop -- you can just call require.


On Thu, Jul 24, 2008 at 9:02 AM, Shadowfirebird
<shadowfirebird@gmail.com> wrote:
> I've had my think.
>
> I think I have some conclusions which might be useful for other people
> in the same boat, and since I've not seen them anywhere else, I hope
> you'll allow me to bore you with them.  No doubt cooler heads than
> mine will see things differently, but there you go.  And, maybe I'm
> missing the obvious, anyway.
>
> 1) require is mildly broken (a).  It doesn't set $" until after the
> given file is loaded.  This can lead to errors when you have a
> circular call of requires. If it set $" first, circular references
> would just be ignored.  Of course, you should never actually *need* to
> have circular 'require' referefences, but: see my next point.
>
> 2) Require is mildly broken (b).  Secondly -- and I suppose that this
> is less of a bug and more of a bugbear -- there is no way to
> distinguish between require-because-it-wont-load-otherwise and
> require-because-some-methods-wont-run-otherwise.  This second sort
> isn't entirely necessary, but it's aesthetically pleasing and useful
> for unit testing.
>
> 3) You can get around (1) by manually pushing the program name into $"
> at the start of each file.  This done, you can use a new idiom -- END
> { require } -- to specify
> require-because-some-methods-wont-run-otherwise.  Not the prettiest
> thing, but neither the ugliest, I think: "in the end, this is
> required."
>
>
> Now I suppose I'd better show my working if I'm going to say anything
> as contentious as all that.  Apologies for the length of this, but
> then, you can stop reading now.  OTOH, I'd really like to hear other
> points of view.
>
> A new set of example programs:
>
> # runner.rb
> require 'root'
> Root.create_data()
> Root.customers.each{|c| puts c.oid, c.name}
>
> # root.rb
> require 'customer'
> class Root
>   @@list = []
>
>   def self.create_data()
>      Customer.new("Dolly")
>      Customer.new("Reymond")
>   end
>
>   def self.customers()
>      return @@list.find_all{|x| x.kind_of?(Customer)}
>   end
>
>   attr_accessor :oid
>
>   def initialize()
>      @oid = @@list.size
>      @@list << self
>   end
> end
>
> # customer.rb
> require 'root'
> class Customer < Root
>   attr_accessor :name
>
>   def initialize(name)
>      super()
>      @name = name
>   end
> end
>
>
> Broadly speaking this follows the same approach as my actual code.  As
> listed, of course, it doesn't work: run runner.rb and it loads
> root.rb, which starts by loading customer.rb, which starts by loading
> root.rb, which...
>
> I needed to make a distinction (#2 above) between code that referred
> to another object when it was loaded; and code that referred to
> another object when it was run.  root.rb doesn't need a 'require
> 'customer'; runner.rb does.  But this is rather unhelpful when it
> comes to unit testing: when writing the test class for Root I
> shouldn't have to remember to require customer.  Ideally I should be
> able to put the require in root.rb somehow.
>
> For experimental purposes lets try putting the "require 'customer'" at
> the *end* of root.rb.  This has practical implications -- no
> programmer is going to look for it there -- but it works; running
> runner.rb produces no errors.   Oddly enough, putting "END {require
> 'customer'}" at the start of the file does not work.  But, wait.
>
> What is more interesting, is that if you run root.rb or customer.rb
> you get warnings about redefined methods. You shouldn't see this if
> require works as described -- a file should never be called twice.
> What appears to be happening is that $" is set after the file is
> loaded -- that is, it's not being set until the chain of requires has
> finished.  We can defeat that behaviour by adding $" << "<filename>"
> to the start of root.rb and customer.rb.  The warnings now disappear.
> (And that seems like a bug to me, or at least an undocumented feature.)
>
> This is really odd: if we now try END{ require 'customer'} at the
> start of root.rb -- well, after the $" thing -- it *works*.  Really
> odd, but nice.
>
> So, root.rb now looks like this:
>
> # root.rb
> $" << "root.rb"
> END { require 'customer' }
> class Root
>   @@list = []
>
>   def self.create_data()
>      Customer.new("Dolly")
>      Customer.new("Reymond")
>   end
>
>   def self.customers()
>      return @@list.find_all{|x| x.kind_of?(Customer)}
>   end
>
>   attr_accessor :oid
>
>   def initialize()
>      @oid = @@list.size
>      @@list << self
>   end
> end
>
> And I can live with that.  But I'm open to suggestions -- any
> suggestions, except rude ones...
>
>



-- 
Me, I imagine places that I have never seen / The colored lights in
fountains, blue and green / And I imagine places that I will never go
/ Behind these clouds that hang here dark and low
But it's there when I'm holding you / There when I'm sleeping too /
There when there's nothing left of me / Hanging out behind the
burned-out factories / Out of reach but leading me / Into the
beautiful sea