From: Eivind Eklund <eeklund@...>
Date: 2004-10-12T00:09:06+09:00
Subject: Re: DI service change notifications (Syringe)

On Mon, 11 Oct 2004 09:12:47 +0900, Jamis Buck <jgb3@email.byu.edu> wrote:
> I guess what I'm feeling is that there is no general way to know,
> definitively, all of the dependencies of a service, especially in a
> dynamic language like Ruby. Without putting restrictions on when and how
> services are defined (like Copland does), I'm not sure how to come up
> with a general solution to this.

I get a feeling you're overengineering here.

Doesn't something like the following work?

class Registry
  def initialize
     @registry = Hash.new
     @active_dependency_registrations = []
     @dependencies = Hash.new
  end
  # This is done by method_missing in Syringe
  def get(symbol)
     register_dependency(symbol)
     retval = nil
     begin
        start_dependency(symbol)
        @registery[symbol].call
     finally
        end_dependency(symbol)
     end
  end
  def register(symbol, &block)
     @registery[symbol] = block
  end
  def start_dependency(symbol)
     if (@active_dependencies.include? symbol)
        raise "Circular dependency"
     else
        @active_dependencies.each do |dependent_symbol|
             @dependencies[dependent_symbol] ||= []
             @dependencies[dependent_symbol] |= [symbol]
        end
        @active_dependencies |= [symbol]
     end
  end
  def end_dependency(symbol)
       @active_dependencies -= [symbol]
  end
end

It builds a dependency tree only inside the present registry.

It only count the directly called methods from call/yield, but that
should be OK for most cases.

And this is just pseudo-code - it's not the way I'd write it for
production (I'd use Set and Hash.default, and handle threads, and ...)

Eivind.