Can't get class name

[Samnang Chhun]

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

 

[Robert Klemme]

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=3DClass.new;p c, c.name;A=3Dc;p c, c.name'
#<Class:0x1005309c>
nil
A
"A"

11:12:50 Temp$ ruby19 -e 'c=3DClass.new;p c,
c.name;Object.const_set("A",c);p c, c.name'
#<Class:0x1005304c>
nil
A
"A"

class Drawing
=A0def initialize(&block)
=A0 =A0instance_eval(&block)
=A0end

=A0def self.const_missing(constant)
=A0 =A0klass =3D Class.new do
=A0 =A0 =A0def self.<(super_klass)
=A0 =A0 =A0 =A0puts "#{self.name} inherits from #{super_klass.name}"
=A0 =A0 =A0end

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.

=A0 =A0 =A0def self.-(association_klass)
=A0 =A0 =A0 =A0puts "#{self.name} has association with
#{association_klass.name}"
=A0 =A0 =A0end
=A0 =A0end

=A0 =A0const_set(constant, klass)
=A0end
end

Drawing.new do

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

=A0Student < Person
=A0Student - Courses
end

Output:
=A0inherits from
=A0has 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 =3D 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.inspec=
t}"
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


--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/