Ara.T.Howard wrote:
...
class JobRunner
class AbstractJobRunner ...
end
class FTPJobRunner < AbstractJobRunner ...
end
class HTTPJobRunner < AbstractJobRunner ...
end
class SCPJobRunner < AbstractJobRunner ...
end
class << self
def new job
klass =
case job.input
when %r|^ftp://|
FTPJobRunner
when %r|^scp://|
SCPJobRunner
when %r|^
http://|
HTTPJobRunner
end
klass::new job
end
end
end
In this kind of situation, I like to try to refactor so that the
switching is done in the subclasses rather than a big case (as I'm sure
you would have done if this had been a real example with a large number
of cases). That can be done, for example, by:
require 'subclass-keeper' # see below
class JobRunner
class AbstractJobRunner
extend SubclassKeeper
def initialize(*args); end
end
class FTPJobRunner < AbstractJobRunner
PAT = %r|^ftp://|
end
class HTTPJobRunner < AbstractJobRunner
PAT = %r|^
http://|
end
class SCPJobRunner < AbstractJobRunner
PAT = %r|^scp://|
end
class << self
def new job
klass = AbstractJobRunner.proper_subclasses.find do |c|
c:
AT === job.input
end
klass::new job
end
end
end
job = Object.new
def job.input; "scp://foo.bar"; end
jr = JobRunner.new job
p jr.class # ==> JobRunner::SCPJobRunner
----- subclass-keeper.rb ----
# Extend a class by SubclassKeeper to record all subclasses (including
itself)
# and make the list available with the #subclasses method.
module SubclassKeeper
def inherited(sub)
super
add_subclass(sub)
end
def add_subclass(sub)
superclass.add_subclass(sub) if superclass.respond_to? :add_subclass
(@proper_subclasses ||= []) << sub
end
protected :add_subclass
def proper_subclasses
(@proper_subclasses ||= []).dup
end
def subclasses
proper_subclasses.unshift(self)
end
end
if __FILE__ == $0
class Base
extend SubclassKeeper
end
class Sub1 < Base; end
class Sub2 < Sub1; end
p Base.subclasses
p Sub1.subclasses
p Sub2.subclasses
end
