I''m trying to dynamically create an instance of an object at runtime,
from a
String. I have a method that returns one of a number of Strings
("Car",
"Motorcycle", "Bicycle"), and when I receive the String, I
then want to
instantiate one of those objects.
Seems like there should be a way to do it in Ruby, but maybe I''ve been
up
too long -- can''t find it. In Java, I''d be doing something
like this:
Class.forName("Car").newInstance();
Any help greatly appreciated.
John
_______________________________________________
John McGrath
http://fryolator.com <http://fryolator.com/>
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2006/1/19, John McGrath <jmcgrath@whoi.edu>:> > > I''m trying to dynamically create an instance of an object at runtime, from a > String. I have a method that returns one of a number of Strings ("Car", > "Motorcycle", "Bicycle"), and when I receive the String, I then want to > instantiate one of those objects. > > Seems like there should be a way to do it in Ruby, but maybe I''ve been up > too long -- can''t find it. In Java, I''d be doing something like this: > > Class.forName("Car").newInstance(); >(eval "Time").new
John McGrath wrote:> I''m trying to dynamically create an instance of an object at runtime, > from a String. I have a method that returns one of a number of Strings > ("Car", "Motorcycle", "Bicycle"), and when I receive the String, I then > want to instantiate one of those objects. > > Seems like there should be a way to do it in Ruby, but maybe I''ve been > up too long -- can''t find it. In Java, I''d be doing something like this: > > Class.forName("Car").newInstance(); > > Any help greatly appreciated. >If you''re classes are in the top level namespace, you can do... Object.const_get( ''Car'' ).new If you''re classes are in another namespace and you know that namespace, you can do the same. module A module B class C end end end c = A::B.const_get( ''C'' ).new Zach
On 1/19/06, John McGrath <jmcgrath@whoi.edu> wrote:> > > I''m trying to dynamically create an instance of an object at runtime, from a > String. I have a method that returns one of a number of Strings ("Car", > "Motorcycle", "Bicycle"), and when I receive the String, I then want to > instantiate one of those objects. > > Seems like there should be a way to do it in Ruby, but maybe I''ve been up > too long -- can''t find it. In Java, I''d be doing something like this: > > Class.forName("Car").newInstance();The other examples so far will work, but in Rails you can simply do: instance = string_containing_class_name.constantize.new e.g. class_name = "Motorcycle" @motorcycle = class_name.constantize.new ..and now, @motorcycle is an instance of Motorcycle.
Take a look at YAML. It makes it trivial to make a whole object graph from a string. On 1/19/06, Wilson Bilkovich <wilsonb@gmail.com> wrote:> On 1/19/06, John McGrath <jmcgrath@whoi.edu> wrote: > > > > > > I''m trying to dynamically create an instance of an object at runtime, from a > > String. I have a method that returns one of a number of Strings ("Car", > > "Motorcycle", "Bicycle"), and when I receive the String, I then want to > > instantiate one of those objects. > > > > Seems like there should be a way to do it in Ruby, but maybe I''ve been up > > too long -- can''t find it. In Java, I''d be doing something like this: > > > > Class.forName("Car").newInstance(); > > The other examples so far will work, but in Rails you can simply do: > instance = string_containing_class_name.constantize.new > > e.g. > class_name = "Motorcycle" > @motorcycle = class_name.constantize.new > > ..and now, @motorcycle is an instance of Motorcycle. > _______________________________________________ > Rails mailing list > Rails@lists.rubyonrails.org > http://lists.rubyonrails.org/mailman/listinfo/rails >