From: Joel VanderWerf <vjoel@...>
Date: 2006-04-27T02:56:27+09:00
Subject: Re: Rake task dependeny vs. method call


I'm really confused about the rest of the examples (it looks to me like
task uidgen is sometimes acting as a "singleton service" and sometimes
as a "parametric service"), but I think I understand this one:

ara.t.howard@noaa.gov wrote:
> as far as i can tell it also fails to detect cycles:
> 
>   harp:~ > cat b.rb
>   require 'tasklib'
> 
>   task :b => :a and task :a => :b
> 
>   b()
> 
> 
>   harp:~ > ruby b.rb
>   ./tasklib.rb:21:in `a': stack level too deep (SystemStackError)
>      from (eval):8:in `a'
>      from ./tasklib.rb:21:in `b'
>      from ./tasklib.rb:21:in `b'
>      from (eval):8:in `b'
>      from ./tasklib.rb:21:in `a'
>      from ./tasklib.rb:21:in `a'
>      from (eval):8:in `a'
>      from ./tasklib.rb:21:in `b'
>       ... 2219 levels...
>      from ./tasklib.rb:21:in `b'
>      from ./tasklib.rb:21:in `b'
>      from (eval):8:in `b'
>      from b.rb:5


This means that we are just using different code :)

Here's mine (pls. excuse the module_eval string argument, it is very old
code), with a stripped down version of T's task code:

module Task
  def cache(method_name)
    module_eval %{
      alias :__compute_#{method_name} :#{method_name}
      def #{method_name}
        if @#{method_name}_cached
          @#{method_name}
        else
          @#{method_name}_cached = true
          @#{method_name} = __compute_#{method_name}
        end
      end
    }
  end

  def task( args, &action )
    if Hash === args
      raise ArgumentError, "#{args.size} for 1" if args.size != 1
      name, *deps = *(args.to_a.flatten)
      name = name.to_sym
      deps = deps.compact.collect{ |e| e.to_sym }
    else
      name, deps = args.to_sym, []
    end

    (@task_dependencies||={})[ name ] = deps

    (class << self; self; end).class_eval do
      define_method( name ) do
        deps.each{ |d| send(d) }
        action.call if action
      end
      cache name
    end
  end
end

include Task

task :b => :a do puts "b" end
task :a => :b do puts "a" end

b()



Output:

a
b

-- 
      vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407