Is this a kind of design patterns?

ruby-talk
1

Hi!

Sometimes a class provides object instantiation methods other than new.
See an example.

class Color
    def initialize r, g, b
        @r = r
        @g = g
        @b = b
    end

    def to_s
        "R: #{@r}, G: #{@g}, B: #{@b}"
    end

    class << self
        def red
            new 255, 0, 0
        end

        def blue
            new 0, 0, 255
        end

        def green
            new 0, 255, 0
        end
    end
end

puts Color.new(100, 120, 140)
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

TIA.

Sam

2

Sam Kong wrote:

Hi!

Sometimes a class provides object instantiation methods other than new.
See an example.

class Color
    def initialize r, g, b
        @r = r
        @g = g
        @b = b
    end

    def to_s
        "R: #{@r}, G: #{@g}, B: #{@b}"
    end

    class << self
        def red
            new 255, 0, 0
        end

        def blue
            new 0, 0, 255
        end

        def green
            new 0, 255, 0
        end
    end
end

puts Color.new(100, 120, 140)
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

TIA.

Sam

isn't that the facory design pattern ?

3

Sam Kong wrote:

Hi!

Sometimes a class provides object instantiation methods other than new.
See an example.

class Color
    def initialize r, g, b
        @r = r
        @g = g
        @b = b
    end

    def to_s
        "R: #{@r}, G: #{@g}, B: #{@b}"
    end

    class << self
        def red
            new 255, 0, 0
        end

        def blue
            new 0, 0, 255
        end

        def green
            new 0, 255, 0
        end
    end
end

puts Color.new(100, 120, 140)
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

Since you invoke a class's method "new" like any other method of any other object (no special syntax) you can say with some justification that all classes are basically factories.

IMHO your example is not optimal because it wastes resources. Since Color is immutable anyway constants seem a better choice:

Color = Struct.new :r, :g, :b
class Color
   def to_s
     sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
   end

   RED = new 0xFF, 0x00, 0x00
   BLUE = new 0x00, 0x00, 0xFF
   GREEN = new 0x00, 0xFF, 0x00
end

Kind regards

  robert

4

That's the "Factory Method" pattern. It's handy when you want
SomeClass.new to return an instance of SomeOtherClass, or just when
you want things to be easier to read.

One of my favorite examples (I think this is a Martin Fowler trick) is:
some_date = december(10,2006)

···

On 3/22/06, Sam Kong <sam.s.kong@gmail.com> wrote:

Hi!

Sometimes a class provides object instantiation methods other than new.
See an example.

class Color
    def initialize r, g, b
        @r = r
        @g = g
        @b = b
    end

    def to_s
        "R: #{@r}, G: #{@g}, B: #{@b}"
    end

    class << self
        def red
            new 255, 0, 0
        end

        def blue
            new 0, 0, 255
        end

        def green
            new 0, 255, 0
        end
    end
end

puts Color.new(100, 120, 140)
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

5

The truth is, as a ganeral rule the original G4 design patterns were kinda
statically-typed-language-centric, so it wouldn't surprise me if there was
some small details in Ruby versions of the patterns that didn't quite fit
the "classic" description.

In this case though, it does look a lot like the Factory pattern, apart from
new still being available. I think if Color.new was re-declared as private,
that would make it a textbook case of the Factory pattern.

IANA(language)L though..

;Daniel

···

On 22/03/06, killy-kun <killy-kun@wanadoo.fr> wrote:

Sam Kong wrote:
> Hi!
>
> Sometimes a class provides object instantiation methods other than new.
> See an example.
>
> class Color
> def initialize r, g, b
> @r = r
> @g = g
> @b = b
> end
>
> def to_s
> "R: #{@r}, G: #{@g}, B: #{@b}"
> end
>
> class << self
> def red
> new 255, 0, 0
> end
>
> def blue
> new 0, 0, 255
> end
>
> def green
> new 0, 255, 0
> end
> end
> end
>
> puts Color.new(100, 120, 140)
> puts Color.red
> puts Color.blue
>
>
> Is this one of design patterns, or just a simple idiom?
> It's similar to a factory method pattern but it's not according to the
> definition.
> Is there any name for it?
>
> TIA.
>
> Sam
>

isn't that the facory design pattern ?

--
Daniel Baird
http://danielbaird.com (TiddlyW;nks! :: Whiteboard Koala :: Blog :: Things
That Suck)
[[My webhost uptime is ~ 92%.. if no answer pls call again later!]]

6

Wilson Bilkovich wrote:

That's the "Factory Method" pattern. It's handy when you want
SomeClass.new to return an instance of SomeOtherClass, or just when
you want things to be easier to read.

One of my favorite examples (I think this is a Martin Fowler trick) is:
some_date = december(10,2006)

At first I thought so.
But the definition of "Factory Method Pattern" bothered me.
The definition of "Factory Method Pattern" is:

"Define an interface for creating an object, but let subclasses decide
which class to instantiate. Factory Method lets a class defer
instantiation to subclasses. "

However, in my Color example, there's no subclassing involved.
So the class itself is a factory as well as the product that the
factory makes.
Do you think that we can still call it "Factory Method Pattern"?

Sam

7

Robert Klemme wrote:

Sam Kong wrote:
> Hi!
>
> Sometimes a class provides object instantiation methods other than new.
> See an example.
>
> class Color
> def initialize r, g, b
> @r = r
> @g = g
> @b = b
> end
>
> def to_s
> "R: #{@r}, G: #{@g}, B: #{@b}"
> end
>
> class << self
> def red
> new 255, 0, 0
> end
>
> def blue
> new 0, 0, 255
> end
>
> def green
> new 0, 255, 0
> end
> end
> end
>
> puts Color.new(100, 120, 140)
> puts Color.red
> puts Color.blue
>
>
> Is this one of design patterns, or just a simple idiom?
> It's similar to a factory method pattern but it's not according to the
> definition.
> Is there any name for it?

Since you invoke a class's method "new" like any other method of any
other object (no special syntax) you can say with some justification
that all classes are basically factories.

IMHO your example is not optimal because it wastes resources. Since
Color is immutable anyway constants seem a better choice:

Color = Struct.new :r, :g, :b
class Color
   def to_s
     sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
   end

   RED = new 0xFF, 0x00, 0x00
   BLUE = new 0x00, 0x00, 0xFF
   GREEN = new 0x00, 0xFF, 0x00
end

This looks tricky and wonderful.
I just tried to make a simple example which was not intended to be
ooptimal.
I will apply your way when I need to make a real code.:slight_smile:
Thank you.

Sam

8

Robert Klemme wrote:

Sam Kong wrote:

    end
        def blue
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

Since you invoke a class's method "new" like any other method of any
other object (no special syntax) you can say with some justification
that all classes are basically factories.

IMHO your example is not optimal because it wastes resources. Since
Color is immutable anyway constants seem a better choice:

Color = Struct.new :r, :g, :b
class Color
   def to_s
     sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
   end

   RED = new 0xFF, 0x00, 0x00
   BLUE = new 0x00, 0x00, 0xFF
   GREEN = new 0x00, 0xFF, 0x00
end

I was thinking along the same lines, but I do like the method interface
(e.g. Color.red over Color::RED). My suggestion would have been
something like:

  class Color
    ...
    class << self
      def red
        @red ||= new 255, 0, 0
      end
      ...
    end
  end

···

--
-- Jim Weirich

--
Posted via http://www.ruby-forum.com/\.

9

Wilson Bilkovich wrote:

···

On 3/22/06, Sam Kong <sam.s.kong@gmail.com> wrote:

Is this one of design patterns, or just a simple idiom? [...]

That's the "Factory Method" pattern. It's handy when you want
SomeClass.new to return an instance of SomeOtherClass, or just when
you want things to be easier to read.

Hmmm ... It's not the GOF Factory Method pattern. It doesn't even solve
the same problem that the Factory Method pattern is designed to address.

But it is a useful technique ... pattern or not.

--
-- Jim Weirich

--
Posted via http://www.ruby-forum.com/\.

10

my personal definition:

factory method:
  method, that creates a object,
  because new(...) is not sufficient
  in that case

imho there's too much babbling about design patterns und too
little pragmatism. who cares if it's pattern #1 or pattern #2.

it's more a matter of good taste as a matter of applying rules.

especially in java I have seen ridiculous numbers of classes doing
trivial stuff using factories, abstract classes, interfaces, proxies,
adapters, delegates and the like. it's often considered by so called
architects to be good software if it uses several design pattern
no matter what for...

···

--- Ursprüngliche Nachricht ---
Von: "Sam Kong" <sam.s.kong@gmail.com>
An: ruby-talk@ruby-lang.org (ruby-talk ML)
Betreff: Re: Is this a kind of design patterns?
Datum: Thu, 23 Mar 2006 01:53:51 +0900

Wilson Bilkovich wrote:
> That's the "Factory Method" pattern. It's handy when you want
> SomeClass.new to return an instance of SomeOtherClass, or just when
> you want things to be easier to read.
>
> One of my favorite examples (I think this is a Martin Fowler trick) is:
> some_date = december(10,2006)

At first I thought so.
But the definition of "Factory Method Pattern" bothered me.
The definition of "Factory Method Pattern" is:

"Define an interface for creating an object, but let subclasses decide
which class to instantiate. Factory Method lets a class defer
instantiation to subclasses. "

However, in my Color example, there's no subclassing involved.
So the class itself is a factory as well as the product that the
factory makes.
Do you think that we can still call it "Factory Method Pattern"?

Sam

11

Is there any difference between the above code and this?

   class Color
     ...
     def self.red
         @red ||= new 255, 0, 0
     end
     ...
   end

···

On 3/22/06, Jim Weirich <jim@weirichhouse.org> wrote:

Robert Klemme wrote:

  class Color
    ...
    class << self
      def red
        @red ||= new 255, 0, 0
      end
      ...
    end
  end

--
R. Mark Volkmann
Object Computing, Inc.

12

Jim Weirich wrote:

Robert Klemme wrote:

Sam Kong wrote:

    end
        def blue
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

Since you invoke a class's method "new" like any other method of any
other object (no special syntax) you can say with some justification
that all classes are basically factories.

IMHO your example is not optimal because it wastes resources. Since
Color is immutable anyway constants seem a better choice:

Color = Struct.new :r, :g, :b
class Color
   def to_s
     sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
   end

   RED = new 0xFF, 0x00, 0x00
   BLUE = new 0x00, 0x00, 0xFF
   GREEN = new 0x00, 0xFF, 0x00
end

I was thinking along the same lines, but I do like the method interface
(e.g. Color.red over Color::RED). My suggestion would have been
something like:

  class Color
    ...
    class << self
      def red
        @red ||= new 255, 0, 0
      end
      ...
    end
  end

And this is tantamount to dependency injection. For example, with my
mindi framework (findable on RAA), there is the examples/color-namespace.rb:

require 'mindi'

class PictureApp
  include MinDI::InjectableContainer

  class Picture
    attr_reader :opts
    def initialize(opts)
      @opts = opts
    end
  end

  class Color < Struct.new(:r, :g, :b)
    def +(color)
      Color.new(r + color.r, g + color.g, b + color.b)
    end
  end

  class ColorNamespace
    include MinDI::InjectableContainer

    red { Color.new(1,0,0) }
    green { Color.new(0,1,0) }
    yellow { red + green }
  end

  colors { ColorNamespace.new }
  picture { Picture.new(:background => colors.yellow) }
end

pic_app = PictureApp.new
pic = pic_app.picture
raise unless pic.opts[:background] == pic_app.colors.yellow

···

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

13

Jim Weirich wrote:

Robert Klemme wrote:

Sam Kong wrote:

    end
        def blue
puts Color.red
puts Color.blue

Is this one of design patterns, or just a simple idiom?
It's similar to a factory method pattern but it's not according to the
definition.
Is there any name for it?

Since you invoke a class's method "new" like any other method of any
other object (no special syntax) you can say with some justification
that all classes are basically factories.

IMHO your example is not optimal because it wastes resources. Since
Color is immutable anyway constants seem a better choice:

Color = Struct.new :r, :g, :b
class Color
   def to_s
     sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
   end

   RED = new 0xFF, 0x00, 0x00
   BLUE = new 0x00, 0x00, 0xFF
   GREEN = new 0x00, 0xFF, 0x00
end

I was thinking along the same lines, but I do like the method interface (e.g. Color.red over Color::RED). My suggestion would have been something like:

  class Color
    ...
    class << self
      def red
        @red ||= new 255, 0, 0
      end
      ...
    end
  end

IMHO this is not thread safe. If you need the method interface, you could do something like

class Color
   def self.method_missing(s,*a,&b)
     if a.empty? && b.nil?
       const_get s.to_s.upcase
     else
       super
     end
   end
end

:slight_smile:

  robert

14

Peter Ertl wrote:

imho there's too much babbling about design patterns und too
little pragmatism. who cares if it's pattern #1 or pattern #2.

The value of patterns is the vocabulary it gives to developers.

it's more a matter of good taste as a matter of applying rules.

especially in java I have seen ridiculous numbers of classes doing
trivial stuff using factories, abstract classes, interfaces, proxies,
adapters, delegates and the like. it's often considered by so called
architects to be good software if it uses several design pattern
no matter what for...

Ahh, now this I agree with. People get it in their heads that patterns
are good, what they forget is that every pattern solves a given problem
with a set of tradeoffs. Understanding the tradeoffs is crucial to
fully understanding the pattern. Too many people blindly apply the full
blown pattern right out of the GOF book without considering the costs.

Beware of programmers who have just learned a new pattern and are
looking for a place to apply it.

···

--
-- Jim Weirich

--
Posted via http://www.ruby-forum.com/\.

15

Peter Ertl wrote:

my personal definition:

factory method:
  method, that creates a object,
  because new(...) is not sufficient
  in that case

imho there's too much babbling about design patterns und too
little pragmatism. who cares if it's pattern #1 or pattern #2.

it's more a matter of good taste as a matter of applying rules.

especially in java I have seen ridiculous numbers of classes doing
trivial stuff using factories, abstract classes, interfaces, proxies,
adapters, delegates and the like. it's often considered by so called
architects to be good software if it uses several design pattern
no matter what for...

You may be right.
However, knowing the right definition is important for communcation.
If somebody tells you to make a class using "X" pattern, you need to
understand what "X" pattern means.
The pattern names might have been arbitrarily made but now it's very
common almost like a standard.

Sam

16

let us wrap
const_get

begin
    const_get(...)
rescue NameError
   super(...)
end
in order to get NoMethodError instead of a NameError

Cheers
Robert

···

On 3/23/06, Robert Klemme <bob.news@gmx.net> wrote:

Jim Weirich wrote:
> Robert Klemme wrote:
>> Sam Kong wrote:
>>> end
>>> def blue
>>> puts Color.red
>>> puts Color.blue
>>>
>>>
>>> Is this one of design patterns, or just a simple idiom?
>>> It's similar to a factory method pattern but it's not according to the
>>> definition.
>>> Is there any name for it?
>> Since you invoke a class's method "new" like any other method of any
>> other object (no special syntax) you can say with some justification
>> that all classes are basically factories.
>>
>> IMHO your example is not optimal because it wastes resources. Since
>> Color is immutable anyway constants seem a better choice:
>>
>> Color = Struct.new :r, :g, :b
>> class Color
>> def to_s
>> sprintf "R: 0x%02x, G: 0x%02x, B: 0x%02x", self.r, self.g, self.b
>> end
>>
>> RED = new 0xFF, 0x00, 0x00
>> BLUE = new 0x00, 0x00, 0xFF
>> GREEN = new 0x00, 0xFF, 0x00
>> end
>
> I was thinking along the same lines, but I do like the method interface
> (e.g. Color.red over Color::RED). My suggestion would have been
> something like:
>
> class Color
> ...
> class << self
> def red
> @red ||= new 255, 0, 0
> end
> ...
> end
> end

IMHO this is not thread safe. If you need the method interface, you
could do something like

class Color
   def self.method_missing(s,*a,&b)
     if a.empty? && b.nil?
       const_get s.to_s.upcase
     else
       super
     end
   end
end

:slight_smile:

        robert

--
Deux choses sont infinies : l'univers et la bêtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

17

Robert Klemme wrote:

IMHO this is not thread safe. If you need the method interface, you
could do something like

[...]

:slight_smile:

I did catch the smiley. :slight_smile:

Given that the original returned a new object on every invocation, a
race condition that might generate an extra light weight object or two
at initialization seems to be a low risk.

However, if I were really concerned about the race condition, I think I
would go the metaprogramming route rather then the dynamic lookup route.
Something more like this:

  class Color
    ...
    class << self
      private
      def define(name, color)
        class_eval "#{name.to_s.upcase} = color"
        class_eval "def Color.#{name}; #{name.to_s.upcase}; end"
      end
    end

    define :red, Color.new(255, 0, 0)
    ...
  end

:wink:

···

--
-- Jim Weirich

--
Posted via http://www.ruby-forum.com/\.

18

No, not at my knowledge

···

On 3/22/06, Mark Volkmann <r.mark.volkmann@gmail.com> wrote:

On 3/22/06, Jim Weirich <jim@weirichhouse.org> wrote:
> Robert Klemme wrote:
>
> class Color
> ...
> class << self
> def red
> @red ||= new 255, 0, 0
> end
> ...
> end
> end

Is there any difference between the above code and this?

   class Color
     ...
     def self.red
         @red ||= new 255, 0, 0
     end
     ...
   end

--

R. Mark Volkmann
Object Computing, Inc.

--
Deux choses sont infinies : l'univers et la bêtise humaine ; en ce qui
concerne l'univers, je n'en ai pas acquis la certitude absolue.

- Albert Einstein

19

Jim Weirich wrote:

Robert Klemme wrote:

IMHO this is not thread safe. If you need the method interface, you
could do something like

[...]

:slight_smile:

I did catch the smiley. :slight_smile:

:slight_smile:

Given that the original returned a new object on every invocation, a race condition that might generate an extra light weight object or two at initialization seems to be a low risk.

However, if I were really concerned about the race condition, I think I would go the metaprogramming route rather then the dynamic lookup route. Something more like this:

  class Color
    ...
    class << self
      private
      def define(name, color)
        class_eval "#{name.to_s.upcase} = color"
        class_eval "def Color.#{name}; #{name.to_s.upcase}; end"
      end
    end

    define :red, Color.new(255, 0, 0)
    ...
  end

:wink:

:slight_smile:

Since we're in Color anyway, you can simplify the definition that by

   class Color
     # ...
     class << self
       private
       def define(name, *args)
         cname = name.to_s.upcase
         col = const_set( cname, new(*args))
         class_eval "def self.#{name}; #{cname}; end"
       end
     end

     define :red, 255, 0, 0
     # ...
   end

:slight_smile:

Kind regards

  robert

20

I have a bunch of template documents which I need to manipulate in very simple ways. I'd like to be able to insert Ruby variables into the template. Here is a very short example:

file fruit_template.txt: This is a fruit: #{fruit}.

fruit = "apple"
f = IO.read("fruit_template.txt")

Then somehow I'd like to end up with this string:
"This is a fruit: apple."

This works fine of course if I construct the string in Ruby:
s = "This is a fruit: #{fruit}."
=> "This is a fruit: apple."

Thanks for any advice.

···

--
- Stephen Bannasch
   Concord Consortium, http://www.concord.org