Some new coverage of an old but favorite quiz.
James Edward G. II
Begin forwarded message:
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/
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