Delegating a method, with arguments

ruby-talk
1

Hi all,

I'm trying to write a class where I want to delegate some instance
methods as FileTest class methods. For example:

require "forwardable"
class Foo < String
   extend Forwardable
   def_delegator(:FileTest,:directory?)
   def initialize(path)
      @path = path
   end
end

This doesn't work, however, since FileTest.directory? requires an
argument. What I would like is something like the following fictional
syntax:

def_delegator(:FileTest,:directory?(@path))

I don't want to create an instance of File and delegate to that
instance because I don't know if @path will actually be valid or not
(among other reasons).

So, would something like this be possible?

Regards,

Dan

2

Not sure I understand, but is this what you are trying to do?

  require "forwardable"
  class Foo < String
     extend Forwardable
     def directory?
       FileTest.directory?(@path)
     end
     def initialize(path)
       @path = path
     end
  end

?

T.

···

On Friday 19 November 2004 12:48 am, Daniel Berger wrote:

Hi all,

I'm trying to write a class where I want to delegate some instance
methods as FileTest class methods. For example:

require "forwardable"
class Foo < String
   extend Forwardable
   def_delegator(:FileTest,:directory?)
   def initialize(path)
      @path = path
   end
end

3

Daniel Berger wrote:

Hi all,

I'm trying to write a class where I want to delegate some instance
methods as FileTest class methods. For example:

require "forwardable"
class Foo < String
   extend Forwardable
   def_delegator(:FileTest,:directory?)
   def initialize(path)
      @path = path
   end
end

If you said that def_delegator always in the form of: def_delegator( class, method, arg1, arg2, arg3, etc... )

Then I think you could do: def_delegator( :FileTest, :directory? , :arg1 )

Or you could do something like: def_delegator( :FileTest, :directory?=>[arg1] )

Zach

4

"Daniel Berger" <djberg96@hotmail.com> schrieb im Newsbeitrag
news:6e613a32.0411182145.45683083@posting.google.com...

Hi all,

I'm trying to write a class where I want to delegate some instance
methods as FileTest class methods. For example:

require "forwardable"
class Foo < String
   extend Forwardable
   def_delegator(:FileTest,:directory?)
   def initialize(path)
      @path = path
   end
end

This doesn't work, however, since FileTest.directory? requires an
argument. What I would like is something like the following fictional
syntax:

def_delegator(:FileTest,:directory?(@path))

I don't want to create an instance of File and delegate to that
instance because I don't know if @path will actually be valid or not
(among other reasons).

So, would something like this be possible?

This is easy but doesn't keep arity:

class Module
  def def_delegator(instance_var, *syms)
    syms.each do |m|
      class_eval "def #{m}(*a,&b) #{instance_var}.#{m}(*a,&b) end"
    end
  end
end

class Foo
  attr_accessor :bar
  def_delegator("@bar", :foo)
end

class Bar
  def foo() "yes" end
end

f=Foo.new

=> #<Foo:0x101a4030>

f.bar = Bar.new

=> #<Bar:0x1019ecc0>

f.foo

=> "yes"

With more effort and the additional info of the target class you can
determine the target method's arity and use that. However, the only
benefit is that clients who ask your delegator method for it's arity see
the real method's arity.

Kind regards

    robert

5

"trans. (T. Onoma)" <transami@runbox.com> wrote in message news:<200411190110.05257.transami@runbox.com>...

···

On Friday 19 November 2004 12:48 am, Daniel Berger wrote:
> Hi all,
>
> I'm trying to write a class where I want to delegate some instance
> methods as FileTest class methods. For example:
>
> require "forwardable"
> class Foo < String
> extend Forwardable
> def_delegator(:FileTest,:directory?)
> def initialize(path)
> @path = path
> end
> end

Not sure I understand, but is this what you are trying to do?

  require "forwardable"
  class Foo < String
     extend Forwardable
     def directory?
       FileTest.directory?(@path)
     end
     def initialize(path)
       @path = path
     end
  end

?

T.

I knew I could do that, but I was trying to find a shortcut rather
than define each method from FileTest manually. However, the syntax
I'm proposing isn't going to save much in terms of keystrokes, so
maybe it isn't worth it after all.

Regards,

Dan

6

It can be done cleanly under 1.9 with Object#instance_eval and
Module#define_method; the syntax would look like
  def_delegator(:FileTest, :directory?){ @path }

Under 1.8, you can easily have something like
  def_delegator(:FileTest, :directory?, :directory?, "@path")
(2nd :directory? for compatibility with forwardable.rb) using
Module#module_eval.

···

On Sat, Nov 20, 2004 at 03:58:10AM +0900, Daniel Berger wrote:

> > I'm trying to write a class where I want to delegate some instance
> > methods as FileTest class methods. For example:
> >
> > require "forwardable"
> > class Foo < String
> > extend Forwardable
> > def_delegator(:FileTest,:directory?)
> > def initialize(path)
> > @path = path
> > end
> > end
>
> Not sure I understand, but is this what you are trying to do?
>
> require "forwardable"
> class Foo < String
> extend Forwardable
> def directory?
> FileTest.directory?(@path)
> end
> def initialize(path)
> @path = path
> end
> end
I knew I could do that, but I was trying to find a shortcut rather
than define each method from FileTest manually. However, the syntax
I'm proposing isn't going to save much in terms of keystrokes, so
maybe it isn't worth it after all.

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