From: Alexander Lamb <Alexander.J.Lamb@...>
Date: 2005-10-14T04:44:11+09:00
Subject: Re: instance from class name?

Thanks for those pointers. The first suggestion worked and since I  
can trust the String of the name of the class, it is ok.

However, I didn't find it in the documentation of the Object class.   
I started on ruby-lang.org then was brought to rubycentral for the  
reference.
Is there another complete reference for ruby 1.8.x? (I am running on  
MacOSX 10.4.2).

Thanks,
--
Alexander Lamb
Service d'Informatique M�dicale
H�pitaux Universitaires de Gen�ve
Alexander.J.Lamb@sim.hcuge.ch
+41 22 372 88 62
+41 79 420 79 73





On Oct 13, 2005, at 9:13 PM, ES wrote:

> David A. Black wrote:
>
>> Hi --
>> On Thu, 13 Oct 2005, Alexander Lamb wrote:
>>
>>> Hello,
>>>
>>> I am new to this list (and language) but I didn't find my answer  
>>> from the documentation available.
>>>
>>> I simply would like to do something like:
>>>
>>> myObject = class.fromName("a_class_name").new
>>>
>
> Classes are stored as constants in ruby. Witness Mr. Black's solution:
>
>
>> my_object = Object.const_get("MyClass").new
>> or some variation of that.
>>
>
> That works; however, if your class name looks like  
> SomeModule::SomeClass,
> you will need to be a bit fancier because const_get only looks for  
> constants
> in the current class or module (the top-level Object instance is  
> the default):
>
>   class_name.split('::').inject(Object) {|parent, obj|  
> parent.const_get obj}.new
>
> #split creates an array ['SomeModule', 'SomeClass'], which we  
> iterate over
> using #inject. In the #inject block, the parent will always be the  
> parent
> class or module in which we look for the constant and obj is the  
> next class
> or module name. The Object is passed in as the initial parent  
> object. the
> parent.const_get obj sequence then looks like
>
>   Object.const_get 'SomeModule' => => SomeModule.const_get 'SomeClass'
>
> There may be a method to directly get the class in the future  
> whether it is
> nested or not. In the meanwhile, you can stick the above code in a  
> method
> if you will be using it a lot.
>
> Also, you can always use #eval:
>
>   obj = eval(class_name).new
>
> Only, of course, if you trust the source of the class_name String. The
> former method is preferred, though.
>
>
>> David
>>
>
> E
>
>
>
>