From: Peter Hickman <peter@...>
Date: 2005-01-17T20:42:08+09:00
Subject: Re: Creating an instance from a variable

Luc Heinrich wrote:

>Peter Hickman <peter@semantico.com> wrote:
>
>  
>
>>        return klass.new(data)
>>    
>>
>
>return Kernel.const_get(klass).new(data)
>
>Note that const_get will throw an exception if the passed class name is
>unknown, so be prepared to deal with that.
>
>  
>
Actually, trying to catch the error seems to be harder than it should 
be. For example:

class Builder
   def Builder.create( klass_sym, data )
        begin
            return Kernel.const_get( klass_sym ).new( data )
        rescue
            raise "There was an error"
        end
   end
end

Should report "There was an error" when const_get fails. However this is 
untrapped.

xx.rb:26:in `const_get': uninitialized constant Bernie at Kernel (NameError)
        from xx.rb:26:in `create'
        from xx.rb:43

I've tried splitting this up into individual steps:

x = Kernel.const_get( klass_sym )
x.new( data )

but this makes no difference.