How to create a class in callers context?

ruby-talk
1

Here's a simple example of my predicament:

class Factory
    def self.generate name,_binding
        _name=name.to_s.capitalize
        eval %[
            class #{_name}
                def to_s
                    "#{_name}"
                end
            end
        ],_binding
    end
end

def Factory_generate what
    Factory.generate what,binding
end

Factory_generate :Thing
puts Factory::Thing.new rescue puts "Can't
Factory::Thing.new" # warning
puts Thing .new rescue puts "Can't Thing.new"

class Universe
    def initialize
        Factory_generate :Planet
        puts Universe::Planet.new rescue puts "Can't
Universe::Planet.new" # warning
        puts Planet .new rescue puts "Can't Planet.new"
    end
end

Universe.new

puts Universe::Planet.new rescue puts "Can't
Universe::Planet.new" # warning
puts Planet .new rescue puts "Can't Planet.new"

···

---------------------------------------------
results in the following surprising output:

C:/Work/class_eval.rb:20: warning: toplevel constant Thing referenced
by Factory::Thing
Thing
Thing
C:/Work/class_eval.rb:26: warning: toplevel constant Planet referenced
by Universe::Planet
Planet
Planet
C:/Work/class_eval.rb:33: warning: toplevel constant Planet referenced
by Universe::Planet
Planet
Planet
----------------------------------------------
Questions:

1) What's the correct way to doing this?
2) I would have thought the non-qualified class references would have
generated exceptions.
3) What is the warning message trying to convey.

2

1) What's the correct way to doing this?

Don't know the "correct" way, there is always more than one form to do
it. This is what I would do

class Class
  def generate(name)
    klass = Class.new
    klass.class_eval <<-EVAL
      def to_s
        "I'm a #{name}"
      end
    EVAL
    const_set(name, klass)
  end
end

class Universe
  generate :Planet
  puts Planet.new
  puts Universe::Planet.new
end

puts Planet.rescue "No Planet!"
puts Universe::Planet.new

···

_______
I'm a Planet
I'm a Planet
No Planet!
I'm a Planet
_______

alternatively you could do

klass = Class.new do
  def foo
    #...
  end
end

but then you can't pass a reference to the variable name. Don't know
if there's a way do do it, though.

If I wanted that to stick on a method, I would pass the binding as
well

class Factory
  def self.generate(name, _binding)
    eval <<-EVAL, _binding
      class #{name}
        def to_s
          "Hello from #{name}"
        end
      end
    EVAL
  end
end

2) I would have thought the non-qualified class references would have
generated exceptions.

Very intriguing. I would have expected the same

3

DMisener wrote:

1) What's the correct way to doing this?
2) I would have thought the non-qualified class references would have
generated exceptions.
3) What is the warning message trying to convey.

Here's my crack at this, not sure this is what you're trying to do:

def generate &name
  eval("self",name.binding).class.class_eval <<-EOS
    class #{name.call}
      def to_s
        name.call
      end
    end
  EOS
end

class Universe
  def initialize
    generate{:Planet}
    puts Universe::Planet
  end
end

generate{:Thing}

Universe.new
puts Thing

···

--
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4

Drew Olson wrote:

DMisener wrote:

1) What's the correct way to doing this?
2) I would have thought the non-qualified class references would have
generated exceptions.
3) What is the warning message trying to convey.

Here's my crack at this, not sure this is what you're trying to do:

Had a small typo, here's the fixed example:

def generate &name
  eval("self",name.binding).class.class_eval <<-EOS
    class #{name.call}
      def to_s
        "#{name.call}"
      end
    end
  EOS
end

class Universe
  def initialize
    generate{:Planet}
  end
end

generate{:Thing}

Universe.new

puts Universe::Planet.new
puts Thing.new

···

--
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