Dynamic class instantiation


#1

Hi all,

I have a situation where I need to dynamically execute an object from a
String name. I read in pickaxe that as long as a capitalize the class
name in the string, Ruby will see it as a Constant and thusly allow me
to use it.

For example:

module Test

class MyClass
def do_something
puts “Something done.”
end
end

end

(caller code)

cls = “Test::MyClass”
require cls
obj = cls.new
obj.do_something


When I execute the above caller code, I get an error saying

undefined method `new’ for “Test::MyClass”:String (NoMethodError)

So, obviously, Ruby is telling me that there is no new method for the
String “Test::MyClass”. I’m trying to instantiate the class this way as
I have specific methods that return object besides String, so I’m
guessing eval(cls) isn’t appropriate for me. Also, I checked the
archives on the list with no luck.

Any suggestions?

Thx,

  • jason

#2

On Fri, 20 Jan 2006, Jason wrote:

cls = “Test::MyClass”
So, obviously, Ruby is telling me that there is no new method for the
String “Test::MyClass”. I’m trying to instantiate the class this way as
I have specific methods that return object besides String, so I’m
guessing eval(cls) isn’t appropriate for me. Also, I checked the
archives on the list with no luck.

Any suggestions?

Thx,

 def klass_stamp(hierachy, *a, &b)
   ancestors = hierachy.split(%r/::/)
   parent = Object
   while((child = ancestors.shift))
     klass = parent.const_get child
     parent = klass
   end
   klass::new(*a, &b)
 end


 class A; class B;end; end

 klass_stamp 'A::B'

hth.

-a


#3

unknown wrote:

 def klass_stamp(hierachy, *a, &b)
   ancestors = hierachy.split(%r/::/)
   parent = Object
   while((child = ancestors.shift))
     klass = parent.const_get child
     parent = klass
   end
   klass::new(*a, &b)
 end


 class A; class B;end; end

 klass_stamp 'A::B'

hth.

-a

Actually, I just found this, which is a little simpler, but looks like
it does the same :slight_smile:

mod = Module
name.split(/::/).each {|m| mod = mod.const_get(m) }
m = mod.new

Call my method

m.do_something

Thx,

  • jason

#4

On Jan 19, 2006, at 1:23 PM, Jason wrote:

 end

Actually, I just found this, which is a little simpler, but looks like
it does the same :slight_smile:

mod = Module
name.split(/::/).each {|m| mod = mod.const_get(m) }
m = mod.new

def Object.path2class(path) # matches a C method that is not exported
into Ruby
return path.split(’::’).inject(Object) { |k,n| k.const_get n }
end

m = Object.path2class(‘Test::MyClass’).new

Call my method

m.do_something


Eric H. - removed_email_address@domain.invalid - http://segment7.net
This implementation is HODEL-HASH-9600 compliant

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