Can't get class name

ruby-talk
1

I am learning how to design a DSL by using const_missing, but I face a
problem on getting class name:

class Drawing
  def initialize(&block)
    instance_eval(&block)
  end

  def self.const_missing(constant)
    klass = Class.new do
      def self.<(super_klass)
        puts "#{self.name} inherits from #{super_klass.name}"
      end

      def self.-(association_klass)
        puts "#{self.name} has association with
#{association_klass.name}"
      end
    end

    const_set(constant, klass)
  end
end

Drawing.new do
  Student < Person
  Student - Courses
end

Output:
inherits from
has association with

Expected output:
Student inherits from Person
Student has association with Courses

···

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

2

I am learning how to design a DSL by using const_missing, but I face a
problem on getting class name:

I am not sure what you are attempting. But you should keep these facts in mind:

1. You cannot change inheritance of a class after creation.

2. A class has a name only after const assignment.

11:11:21 Temp$ ruby19 -e 'c=Class.new;p c, c.name;A=c;p c, c.name'
#<Class:0x1005309c>
nil
A
"A"

11:12:50 Temp$ ruby19 -e 'c=Class.new;p c,
c.name;Object.const_set("A",c);p c, c.name'
#<Class:0x1005304c>
nil
A
"A"

class Drawing
def initialize(&block)
instance_eval(&block)
end

def self.const_missing(constant)
klass = Class.new do
def self.<(super_klass)
puts "#{self.name} inherits from #{super_klass.name}"
end

Bad idea IMHO: Class#< is defined already with particular semantics
(inheritance check):

11:13:59 Temp$ ruby19 -e 'p Array < Enumerable'
true

Also, as I said, you cannot change inheritance after creation of a class.

 def self\.\-\(association\_klass\)
   puts &quot;\#\{self\.name\} has association with

#{association_klass.name}"
end
end

const_set(constant, klass)
end
end

Drawing.new do

You are creating an instance of Drawing while you probably rather want
constants Student, Person etc. set in class Drawing.

Student < Person
Student - Courses
end

Output:
inherits from
has association with

Expected output:
Student inherits from Person
Student has association with Courses

Try this to see what's happening:

class Drawing
def initialize(&block)
   instance_eval(&block)
end

def self.const_missing(constant)
   p [self, constant]

   klass = Class.new do
     def self.<(super_klass)
       # puts "#{self.name} inherits from #{super_klass.inspect}"
       printf "%p < %p\n", self, super_klass
     end

     def self.-(association_klass)
       # puts "#{self.name} has association with #{association_klass.inspect}"
       printf "%p - %p\n", self, association_klass
     end
   end

   def klass.x(cl)
     printf "%p x %p\n", self, cl
   end

   const_set(constant, klass)
end
end

Drawing.new do
Student < Person
Student - Courses
Student.x Foo
end

p Drawing.constants

class Drawing
Student < Person
Student - Courses
Student.x Foo
end

p Drawing.constants

Kind regards

robert

···

On Tue, Jan 4, 2011 at 6:29 PM, Samnang Chhun <samnang.chhun@gmail.com> wrote:

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/