Enumerating constants in anonymous modules


#1

How can I enumerate all the constants inside the module in the second
example?
Notice that #constants array is empty

For bonus points, which is the “correct” eval method to use to define a
class inside the module (they all seem to work)

Cheers,
Xavier

module Foo
class A
end
end

puts Foo.constants.inspect # => [“A”]

[:module_eval, :instance_eval, :class_eval].each do |method|
m = Module.new
m.send(method) do
class B
end
end
puts m.constants.inspect # => [] (I would expect [‘B’])
puts m.const_get(‘B’).inspect # => B
end


#2

Hi –

On Fri, 10 Oct 2008, Xavier S. wrote:

How can I enumerate all the constants inside the module in the second
example?
Notice that #constants array is empty

See comments in code, below.

For bonus points, which is the “correct” eval method to use to define a
class inside the module (they all seem to work)

module_eval and class_eval are synonyms for each other. I’d use
module_eval over instance_eval, unless you specifically need instance
methods to be singleton methods on the module object (which is
unlikely, and can be achieved by other means under module_eval).

class B
The constant B is resolved in the usual “semi-static”, eager way,
which means it does not belong to the new module: it’s actually being
defined at the top level.

end
end
puts m.constants.inspect # => [] (I would expect [‘B’])
puts m.const_get(‘B’).inspect # => B
end

Try this:

m = Module.new
m.module_eval do
class self::B # forces Ruby to wait to bind the constant
end
end
puts m.constants.inspect # [“B”]
puts m.const_get(‘B’).inspect # #Module:0x220164::B

David


#3

David A. Black wrote:

Hi –

On Fri, 10 Oct 2008, Xavier S. wrote:

How can I enumerate all the constants inside the module in the second
example?
Notice that #constants array is empty

See comments in code, below.

For bonus points, which is the “correct” eval method to use to define a
class inside the module (they all seem to work)

module_eval and class_eval are synonyms for each other. I’d use
module_eval over instance_eval, unless you specifically need instance
methods to be singleton methods on the module object (which is
unlikely, and can be achieved by other means under module_eval).

I’m not really sure what I need, I’ll do some more reading and come back
if I have any further questions. Using module_eval for now.

Try this:

m = Module.new
m.module_eval do
class self::B # forces Ruby to wait to bind the constant
end
end
puts m.constants.inspect # [“B”]
puts m.const_get(‘B’).inspect # #Module:0x220164::B

This does what I want, cheers