From: James French <James.French@...>
Date: 2012-04-05T23:25:18+09:00
Subject: Re: Design pattern question



-----Original Message-----
From: Robert Klemme [mailto:lists@ruby-forum.com] 
Sent: 05 April 2012 14:20
To: ruby-talk ML
Subject: Re: Design pattern question

James French wrote in post #1055131:
> Its pretty simple really. I want to be able to call an API like this:
>
> SourceControl.checkout
> SourceControl.update

You better do

sc.checkout
sc.update

i.e. not use a constant but an instance variable.

> I want to be able to plugin different source control systems that 
> conform to the API.

Well, in Ruby there are no interfaces so you can, but do not need to use inheritance.

> My initial thought was just to go with a simple C++ style 
> wrapper/delegate approach:
>
> module SourceControl
>
> def self.checkout(repository, dest, options={})
>   @sourceControl.checkout(repository, dest, options) end
>
> def self.update(path, options={})
>   @sourceControl.update(parth, options) end
>
> class SourceControlAPI
>
>   def checkout(repository, dest, options={})
>   end
>
>   def update(path, options={})
>   end
>
> end
>
> end
>
> But I bet there is a nicer way, perhaps without having to duplicate 
> the API?

Especially, what advantages does it have?

I'd probably simply do

class CVS
  def checkout(dest, options={})
  end

  def update(path, options={})
  end
end

class SVN
  def checkout(dest, options={})
  end

  def update(path, options={})
  end
end

class Perforce
  def checkout(dest, options={})
  end

  def update(path, options={})
  end
end

and then

# connection
sc = SVN.new("svn-repo.my.network.com", "James", "p@ssword")

# repository
sc.checkout("repo", "/tmp/work") do |repo|
  repo.update("foo")
  File.open(repo.path + "foo", "a") {|io| io.write("a change)}
  repo.submit("foo")
end # auto commit

sc.close # needed?

You could even make SVN.new accept a block which receives "sc" and cleans up in ensure regardless how the block terminates.

http://blog.rubybestpractices.com/posts/rklemme/002_Writing_Block_Methods.html

Kind regards

robert


Using  the Jay Fields link and slightly modifying I've got something I'm happy with. Thanks for the help Robert, as always :)

module SourceControl
  def self.init(subject)
    subject.public_methods(false).each do |meth|
      (class << self; self; end).class_eval do
        define_method meth do |*args|
          subject.send meth, *args
        end
      end
    end
  end
end

class SourceControlAPI
  
  def checkout(repository, dest, options={})
  end
  
  def update(path, options={})
  end
  
end

class SVN < SourceControlAPI
  
  def checkout(repository, dest, options={})
    puts "Checking out from SVN"
  end
  
  def update(path, options={})
  end
  
end

SourceControl.init(SVN.new)
SourceControl.checkout('foo', 'bar')