From: Joel VanderWerf <vjoel@...>
Date: 2006-04-26T14:13:34+09:00
Subject: Re: Rake task dependeny vs. method call

ara.t.howard@noaa.gov wrote:
> On Wed, 26 Apr 2006, Trans wrote:
> 
>> Just for fun I put together this simple demonstration.
> 
> check out tsort.  you need it to work if you have a diamond like
> 
>   b => a
>   c => a
>   d => b
>   d => c
> 
> else you'll run 'a' twice.  tsort let's you build a dag of dependancies and
> even detects cycles.
> 
> cheers.
> 
> 
> -a

He (OP) already did the t-sort, implicitly.

Here's a slightly modified version of T's code (#cache happens to be the
name of #memoize in my libs). The output is:

a
b
c

----------------------
require 'cache'

module Task

  # Store the dependencies.

  def task_dependencies
    @task_dependencies ||= {}
  end

  # Store the decriptions.

  def task_descriptions
    @task_descriptions ||= {}
  end

  # Set the description of the subsequent task.

  def desc( line )
    @last_description = line.gsub("\n",'')
  end

  # Define a task.

  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
    task_descriptions[ name ] = @last_description
    @last_description = nil

    (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 :a do puts "a" end
task :b => :a do puts "b" end
task :c => :a do puts "c" end
task :d => [:b, :c]

d


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