# Fwd: Ruby Quiz Corrections

**URL:** <https://www.ruby-forum.com/t/fwd-ruby-quiz-corrections/84634>\
**Category:** Ruby\
**Created:** [February 6, 2007, 5:13pm UTC](https://www.ruby-forum.com/t/fwd-ruby-quiz-corrections/84634 "2007-02-06T17:13:38Z")\
**Posts on this page:** 2\
**Page:** 1

<div class="post-metadata">

**Author:** ![bbazzarrakk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/47e85d/32.png) [@bbazzarrakk](https://www.ruby-forum.com/u/bbazzarrakk)\
**Post date:** [February 6, 2007, 5:13pm UTC](https://www.ruby-forum.com/t/fwd-ruby-quiz-corrections/84634/1 "2007-02-06T17:13:38Z")

</div>

Some new coverage of an old but favorite quiz.

James Edward G. II

Begin forwarded message:

---

<div class="post-metadata">

**Author:** ![bbazzarrakk](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/b/47e85d/32.png) [@bbazzarrakk](https://www.ruby-forum.com/u/bbazzarrakk)\
**Post date:** [February 6, 2007, 5:49pm UTC](https://www.ruby-forum.com/t/fwd-ruby-quiz-corrections/84634/2 "2007-02-06T17:49:43Z")

</div>

On Tue, 6 Feb 2007, James Edward G. II wrote:

> Some new coverage of an old but favorite quiz.

thanks james

> > behind). Anyways, I think that the koans are missing or have incorrect  
> > assertions.
> > 
> > I’m not sure if you post corrections, or if you can forward this on to the  
> > author, but I posted some of the problems that I discovered while solving  
> > the quiz at [http://kinderman.net/articles/2007/02/05/](http://kinderman.net/articles/2007/02/05/)  
> > problems-with-the-metakoans-rb-ruby-quiz.

hi ryan-

yeah. interesting point. in fact, you are right but for reasons you  
might  
not suspect. regarding the

assert{ (o.a = nil) == nil }

assertions you’ll note they all start when default values are being  
provided,  
what’d i’d meant to testing here was that the setter should always  
return the  
new value and not the one provided as a default. obviously that’s a  
mistake  
since, in ruby, setters always do this, one cannot change it:

harp:~ \> cat a.rb  
def a=(x) 42 end  
p(self.a = ‘forty-two’)

harp:~ \> ruby a.rb  
“forty-two”

so the best thing would be to simple remove those test or, as you point  
out,  
do a two step test. i chose the latter for the new version.

regarding incrementing 42 - that’s impossible! 😉 see if you like my  
new  
approach. it acheives the same end goal, which is valuable:

harp: ~\> cat a.rb

# 

# metakoans.rb is an arduous set of exercises designed to stretch

# meta-programming muscle. the focus is on a single method

‘attribute’ which

# behaves much like the built-in ‘attr’, but whose properties require

deleving

# deep into the depths of meta-ruby. usage of the ‘attribute’ method

follows

# the general form of

# 

# class C

# attribute ‘a’

# end

# 

# o = C::new

# o.a = 42 # setter

# o.a # getter

# o.a? # query

# 

# but reaches much farther than the standard ‘attr’ method as you

will see

# shortly.

# 

# your path, should you choose to follow it, is to write a single

file

# ‘knowledge.rb’ implementing all functionality required by the koans

below.

# as a student of meta-programming your course will be guided by a

guru whose

# wisdom and pithy sayings will assist you on your journey.

# 

# a successful student will eventually be able to do this

# 

# harp:~ \> ruby metakoans.rb knowledge.rb

# koan\_1 has expanded your awareness

# koan\_2 has expanded your awareness

# koan\_3 has expanded your awareness

# koan\_4 has expanded your awareness

# koan\_5 has expanded your awareness

# koan\_6 has expanded your awareness

# koan\_7 has expanded your awareness

# koan\_8 has expanded your awareness

# koan\_9 has expanded your awareness

# mountains are again merely mountains

# 

module MetaKoans

# 

# ‘attribute’ must provide getter, setter, and query to instances

# 

```
 def koan_1
   c = Class::new {
     attribute 'a'
   }

   o = c::new

   assert{ not o.a? }
   assert{ o.a = 31 }
   assert{ o.a == 31 }
   assert{ o.a? }
 end

```

# 

# ‘attribute’ must provide getter, setter, and query to classes

# 

```
 def koan_2
   c = Class::new {
     class << self
       attribute 'a'
     end
   }

   assert{ not c.a? }
   assert{ c.a = 32 }
   assert{ c.a == 32 }
   assert{ c.a? }
 end

```

# 

# ‘attribute’ must provide getter, setter, and query to modules at

module

# level

# 

```
 def koan_3
   m = Module::new {
     class << self
       attribute 'a'
     end
   }

   assert{ not m.a? }
   assert{ m.a = 33 }
   assert{ m.a == 33 }
   assert{ m.a? }
 end

```

# 

# ‘attribute’ must provide getter, setter, and query to modules which

operate

# corectly when they are included by or extend objects

# 

```
 def koan_4
   m = Module::new {
     attribute 'a'
   }

   c = Class::new {
     include m
     extend m
   }

   o = c::new

   assert{ not o.a? }
   assert{ o.a = 34 }
   assert{ o.a == 34 }
   assert{ o.a? }

   assert{ not c.a? }
   assert{ c.a = 35 }
   assert{ c.a == 35 }
   assert{ c.a? }
 end

```

# 

# ‘attribute’ must provide getter, setter, and query to singleton

objects

# 

```
 def koan_5
   o = Object::new

   class << o
     attribute 'a'
   end

   assert{ not o.a? }
   assert{ o.a = 36 }
   assert{ o.a == 36 }
   assert{ o.a? }
 end

```

# 

# ‘attribute’ must provide a method for providing a default value as

hash

# 

```
 def koan_6
   c = Class::new {
     attribute 'a' => 37
   }

   o = c::new

   assert{ o.a == 37 }
   assert{ o.a? }
   assert{ o.a = nil; o.a == nil }
   assert{ not o.a? }
 end

```

# 

# ‘attribute’ must provide a method for providing a default value as

block

# which is evaluated at instance level

# 

```
 def koan_7
   c = Class::new {
     attribute('a'){ b }
     def b
       38
     end
   }

   o = c::new

   assert{ o.b == 38 }
   assert{ o.a == 38 }
   assert{ o.a? }
   assert{ o.a = nil; o.a == nil }
   assert{ not o.a? }
   assert{ o.b == 38 }
 end

```

# 

# ‘attribute’ must provide inheritence of default values at both

class and

# instance levels

# 

```
 def koan_8
   b = Class::new {
     class << self
       attribute 'a' => 39
       attribute('b'){ a }
     end
     attribute 'a' => 40
     attribute('b'){ a }
   }

   c = Class::new b

   assert{ c.b == 39 }
   assert{ c.a == 39 }
   assert{ c.a? }
   assert{ c.a = nil; c.a == nil }
   assert{ not c.a? }
   assert{ c.b == 39 }

   o = c::new

   assert{ o.b == 40 }
   assert{ o.a == 40 }
   assert{ o.a? }
   assert{ o.a = nil; o.a == nil }
   assert{ not o.a? }
   assert{ o.b == 40 }
 end

```

# 

# into the void

# 

```
 def koan_9
   b = Class::new {
     class << self
       attribute 'a' => 41
       attribute('b'){ a }
     end
     include Module::new {
       attribute 'a' => 42
       attribute('b'){ a }
     }
   }

   c = Class::new b

   assert{ c.b == 41 }
   assert{ c.a == 41 }
   assert{ c.a? }
   assert{ c.a = nil; c.a == nil }
   assert{ not c.a? }
   assert{ c.b == 41 }

   o = c::new

   assert{ o.b == 42 }
   assert{ o.a == 42 }
   assert{ o.a? }
   assert{ o.a = nil; o.a == nil }
   assert{ not o.a? }
   assert{ o.b == 42 }
 end

 def assert() raise unless yield end

```

end

class MetaStudent  
def initialize knowledge  
require knowledge  
end  
def ponder koan  
begin  
send koan  
true  
rescue =\> e  
STDERR.puts %Q[#{ e.message } (#{ e.class })\n#{  
e.backtrace.join 10.chr }]  
false  
end  
end  
end

class MetaGuru  
require “singleton”  
include Singleton

```
 def enlighten student
   student.extend MetaKoans

   koans = student.methods.grep(%r/koan/).sort

   attainment = nil

   koans.each do |koan|
     awakened = student.ponder koan
     if awakened
       puts "#{ koan } has expanded your awareness"
       attainment = koan
     else
       puts "#{ koan } still requires meditation"
       break
     end
   end

   puts(
     case attainment
       when nil
         "mountains are merely mountains"
       when 'koan_1', 'koan_2'
         "learn the rules so you know how to break them properly"
       when 'koan_3', 'koan_4'
         "remember that silence is sometimes the best answer"
       when 'koan_5', 'koan_6'
         "sleep is the best meditation"
       when 'koan_7'
         "when you lose, don't lose the lesson"
       when 'koan_8'
         "things are not what they appear to be: nor are they 

```

otherwise"  
else  
“mountains are again merely mountains”  
end  
)  
end  
def self::method\_missing m, \*a, &b  
instance.send m, \*a, &b  
end  
end

knowledge = ARGV.shift or abort “#{ $0 } knowledge.rb”  
student = MetaStudent::new knowledge  
MetaGuru.enlighten student

-a