Meta-programming in Ruby : Part 2 : Method Missing

Code 1

class Hash
    def method_missing(m,*a)
        if m.to_s =~ /=$/
          self[$`] = a[0]
        elsif a.empty?
          self[m]
        else
          raise NoMethodError, "#{m}"
        end
    end
end

x = {'abc' => 123}
p x['abc']
print "\n"

x.foo = :baz
x.goo = "duh"
x.x&z = 10
p x

Result 1

[root@localhost ruby_tutor]# ruby method_missing1.rb
123

{"abc"=>123, "foo"=>:baz, "goo"=>"duh"}

Code 2

class Hunt
   @@arr = []
   def show;
       @@arr;
   end

   def method_missing(name, *args)
      begin
           @@arr.send(name, *args)
      rescue
          "'#{name}' method has NOT been implemented YET"
      end
   end
end

he = Hunt.new

he << 123
he << "Be happy, Son!"
p he.show
puts he.flyswim

Result 2

[123, "Be happy, Son!"]
'flyswim' method has NOT been implemented YET

Code 3
Remember that method_missing will provide a block if one is given

def method_missing(name, *args, &block)
  block.call(*args) if block_given?
end

no_method("Ask","why", "study this !"){ |*args| p args }

Result 3

[root@localhost ruby_tutor]# ruby  method_missing_bloc_CROSS-REF.rb
["Always demand", "why you have to", "study this or that or whatever!"]

Meta-programming in Ruby : Part 1 : Alias

There are altogether 16 posts on this topic of meta-programming in Ruby language. Our approach encourages hands-on experimentation. The exercises here are specially designed to facilitate self-study and other independent modes of learning.

Provided we can find time amidst our busy schedule(well, who is not busy these days?), we will also discuss meta-programming in other languages such as Lisp and python.

Code 1

class A
 def fan;
     puts "fan";
 end
def feast;
     puts "feast";
 end
end
a= A.new
a.fan
a.feast
class A
 alias :flank :fan
 alias :foo :feast
 private :fan
end
begin
a.fan
rescue
 puts ">>>>>>   private method `fan' called for #",
      ">>>>>>   Accessible unless declared \"private\" as above"
end
a.feast
a.foo
a.flank
puts "\n\n"

class Z
 attr_accessor :gear
 alias :get_gear    :gear
 alias :set_gear    :gear=
end

zoe =Z.new
zoe.gear = 34
puts zoe.gear

zoe.set_gear(34)
puts zoe.get_gear 

Results 1

[root@localhost ruby_tutor]# ruby 1alias.rb
fan
feast
>>>>>>   private method `fan' called for #
>>>>>>   Accessible unless declared "private" as above
feast
feast
fan


34
34

Code 2

class String
   alias_method :original_reverse, :reverse

   def reverse
     "Trying to reverse, please wait ... "+ original_reverse
   end
end
p "happy holy days".original_reverse

p "happy holy days".reverse

Results 2

[root@localhost ruby_tutor]# ruby   2alias_method1.rb
"syad yloh yppah"
"Trying to reverse, please wait ... syad yloh yppah"