# Attributes-3.3.0

**URL:** <https://www.ruby-forum.com/t/attributes-3-3-0/105976>\
**Category:** Ruby\
**Created:** [June 5, 2007, 5:31am UTC](https://www.ruby-forum.com/t/attributes-3-3-0/105976 "2007-06-05T05:31:54Z")\
**Posts on this page:** 1\
**Page:** 1

<div class="post-metadata">

**Author:** ![ara.t.howard](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/a8b319/32.png) [@ara.t.howard](https://www.ruby-forum.com/u/ara.t.howard)\
**Post date:** [June 5, 2007, 5:31am UTC](https://www.ruby-forum.com/t/attributes-3-3-0/105976/1 "2007-06-05T05:31:54Z")

</div>

NAME  
attributes.rb

INSTALL  
gem install attributes

URIS  
[http://rubyforge.org/projects/codeforpeople/](http://rubyforge.org/projects/codeforpeople/)  
[http://codeforpeople.com/lib/ruby](http://codeforpeople.com/lib/ruby)

SYNOPSIS  
attributes.rb provides a set of attr\_\* like method with several user  
friendly additions. attributes.rb is similar to the traits.rb  
package but  
sacrifices a few features for simplicity of implementation:  
attributes.rb is  
only 42 lines of code.

the implimentation of attributes.rb borrows many of the best ideas  
from the  
metakoans.rb ruby quiz

```
 http://www.rubyquiz.com/quiz67.html

```

in particular the solutions of Christian N. and Florian  
Gross.

HISTORY  
3.3.0

```
 moved to an instance variable-less model using an module level

```

closure for  
the attributes list

SAMPLES

\<========\< samples/a.rb \>========\>

~ \> cat samples/a.rb

```
 #
 # basic usage is like attr, but note that attribute defines

```

three methods,  
# getter, setter, and query  
#  
require ‘attributes’

```
   class C
     attribute 'a'
   end

   c = C.new

   c.a = 42 # setter
   p c.a # getter
   p 'forty-two' if c.a? # query

 #
 # also not that attribute(s) works as well for objects as classes
 #
   o = Object.new
   o.attribute 'answer' => 42
   p o.answer

```

~ \> ruby samples/a.rb

```
 42
 "forty-two"
 42

```

\<========\< samples/b.rb \>========\>

~ \> cat samples/b.rb

```
 #
 # default values may be given either directly or as a block

```

which will be  
# evaluated in the context of self. in both cases (value or  
block) the  
# default is set only once and only if needed - it’s a lazy  
evaluation.  
#  
require ‘attributes’

```
   class C
     attribute :a => 42
     attribute(:b){ Float a }
   end

   c = C.new

   p c.a
   p c.b

```

~ \> ruby samples/b.rb

```
 42
 42.0

```

\<========\< samples/c.rb \>========\>

~ \> cat samples/c.rb

```
 #
 # multiple values may by given, plain names and key/val pairs

```

may be mixed.  
#  
require ‘attributes’

```
   class C
     attributes 'x', 'y' => 0b101000, 'z' => 0b10
   end

   c = C.new
   c.x = c.y + c.z
   p c.x

```

~ \> ruby samples/c.rb

```
 42

```

\<========\< samples/d.rb \>========\>

~ \> cat samples/d.rb

```
 #
 # a nice feature is that all attributes are enumerated in the

```

class. this,  
# combined with the fact that the getter method is defined so as  
to delegate  
# to the setter when an argument is given, means bulk  
initialization and/or  
# attribute traversal is very easy.  
#  
require ‘attributes’

```
   class C
     attributes %w( x y z )

     def attributes
       self.class.attributes
     end

     def initialize
       attributes.each_with_index{|a,i| send a, i}
     end

     def to_hash
       attributes.inject({}){|h,a| h.update a => send(a)}
     end

     def inspect
       to_hash.inspect
     end
   end

   c = C.new
   p c.attributes
   p c

   c.x 'forty-two'
   p c.x

```

~ \> ruby samples/d.rb

```
 ["x", "y", "z"]
 {"x"=>0, "y"=>1, "z"=>2}
 "forty-two"

```

\<========\< samples/e.rb \>========\>

~ \> cat samples/e.rb

```
 #
 # my favourite element of attributes is that getters can also be

```

setters.  
# this allows incredibly clean looking code like  
#  
require ‘attributes’

```
   class Config
     attributes %w( host port)
     def initialize(&block) instance_eval &block end
   end

   conf = Config.new{
     host 'codeforpeople.org'

     port 80
   }

   p conf

```

~ \> ruby samples/e.rb

```
 #<Config:0x220b0 @port=80, @host="codeforpeople.org">

```

enjoy.

-a