Creating classes dynamically?

ruby-talk
1

hello

I would like to create classes dynamically and also the name of the class

somethink like that

cl = Class.new(“Eagle”) # does not work

bird = Eagle.new
bird.fly()

can this be done ? I want many classes to be created and the names come from
config files or the command line

Markus

2

cl = Class.new("Eagle") # does not work

   Eagle = Class.new # the argument to Class::new is the superclass

can this be done ? I want many classes to be created and the names come from
config files or the command line

svg% ruby -e 'Object.const_set("Eagle", Class.new); p Eagle.class'
Class
svg%

Guy Decoux

3

here are some ideas:

~ > cat bird.rb
#!/usr/bin/env ruby

birdname = ARGV[0] || ‘Eagle’

this allows a class with attributes only…

attributes = :wing_span, :age
Birdclass = Struct.new birdname, *attributes
bird = Birdclass.new
bird.wing_span = 42.0

you could then add methods to the object like this:

class << bird
def fly; ‘fly’; end
end
p bird.fly

or perhaps it’d be better to add it to the class up front

module BirdModule
def fly; ‘Fly’; end
end
Birdclass2 = Struct.new birdname, *attributes
Birdclass2.send :include, BirdModule
bird = Birdclass2.new
bird.wing_span = 42.0
p bird.fly

alternatively, you could create libfiles and require them

this could be really helpful for debugging purposes and could

also allow caching of classes between invocations…

module Bird; BIRD_CLASSES = {}; end

classdef = <<-‘ruby’
module Bird
class %s
attr_accessor :wing_span
attr_accessor :age
def fly; ‘FLY’; end
end

BIRD_CLASSES[‘%s’] = %s
end
ruby

lib = ‘./birdlib.rb’
open(lib,‘w’){|f| f.puts(classdef % [birdname, birdname, birdname])}
require lib
birdclass = Bird::BIRD_CLASSES[birdname]
bird = birdclass.new
bird.wing_span = 42.0
p bird.fly

~ > ruby bird.rb
“fly”
“Fly”
“FLY”

i like the last one best for it’s debugging, testing, and caching
capabilities… any method which creates a class dynamically is hard to test -
this way you could test any of the created classes using the cached libs…

-a

···

On Sat, 14 Jun 2003, Markus Jais wrote:

hello

I would like to create classes dynamically and also the name of the class

somethink like that

cl = Class.new(“Eagle”) # does not work

bird = Eagle.new
bird.fly()

can this be done ? I want many classes to be created and the names come from
config files or the command line

–

Ara Howard
NOAA Forecast Systems Laboratory
Information and Technology Services
Data Systems Group
R/FST 325 Broadway
Boulder, CO 80305-3328
Email: ara.t.howard@noaa.gov
Phone: 303-497-7238
Fax: 303-497-7259
~ > ruby -e ‘p(%.\x2d\x29…intern)’
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