From: Robert Klemme <shortcutter@...>
Date: 2009-03-30T00:54:57+09:00
Subject: Re: Dynamic object creation in ruby

On 29.03.2009 16:38, Pascal J. Bourguignon wrote:
> Robert Klemme <shortcutter@googlemail.com> writes:
> 
>> On 29.03.2009 13:40, Brian Candler wrote:
>>>> frank = Object.const_get("Master::Person").new("Frank")
>>>>
>>>> Does anyone know why the second way fails?
>>> frank = Master.const_get("Person").new("Frank")
>> Erm, that's a hybrid solution.  If you know the names beforehand, you
>> can just do
>>
>> frank = Master::Person.new "Frank"
> 
> Then the answer for the OP would be:
> 
> frank = Object.const_get("Master").const_get("Person").new("Frank")

Why would anyone want to use Strings when he knows the names (and 
consequently their number) beforehand?  That does not make sense.

> const_get takes only a simple constant name, not a qualified name.

Yes, and that's why the solutions that were provided use some form of 
String#split to cut a fully qualified name down to individual constants.

>> I would assume that the OP receives the full qualified name as a
>> String and wants to get the class from there which can only be
>> achieved with any of the other solutions shown.
> 
> Obviously, he wants to replace the literals by variables.

Apart from the plurals:

> This works:
> 
> john = eval("Master::Person").new("John")
> 
> This fails:
> 
> frank = Object.const_get("Master::Person").new("Frank")

Regards

	robert