comp.lang.ruby

nobu.nokada

11/27/2003 11:18:00 AM

Hi,

At Tue, 25 Nov 2003 23:26:58 +0900,
Ceri Storey wrote:
> Am I correct in thinking that the #inherited method of the parent class
> is called *before* the body of the class is evaluated?

Yes. The end of definition cannot be determined in Ruby.

> If so, is there a more sensible way of working around this, than
> something like the following?

I thought of similar one formerly, and still haven't get better
one.

Well, how about #singleton_method_added, if you use particular
singleton method as the key?
# But note that Module#name is pre-defined method.

class Builder
@@registry = {}
class << self
def singleton_method_added(name)
@@registry[send(name)] = self if name == :name
super
end

def lookup(name)
@@registry.fetch(name) do
raise ArgumentError, "No such Class"
end
end

def create(name, *args)
lookup(name).new(*args)
end
end
end

class Moogle < Builder
def self.name
"moogle"
end
end

Builder.create("moogle")

Or, if names are always class names in lower case, you can use
the names even in #inherited.

class Builder
@registry = {}
class << self
def inherited(c)
@registry[c.name.downcase] = c
super
end

def lookup(name)
@registry.fetch(name) do
raise ArgumentError, "No such Class"
end
end
end

You can define Builder.name as returning lower case name and
use it too.

class Builder
@registry = {}
class << self
def name
super.downcase
end
def inherited(c)
@registry[c.name] = c
super
end
end
end

And another one, with http://nokada.jin.gr.jp/ruby/...

require 'factory'

class Builder
extend Factory
end

class Moogle < Builder
factory do |name, *args|
new(*args) if /\Amoogle\z/ =~ name
end
end

p Builder.create("moogle")

--
Nobu Nakada