Forum: Ruby dynamic object creation

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Ken T. (Guest)
on 2009-05-25 20:58
sorry if i've missed something obvious

is there a way in ruby to dynamically create an object from a variable
that holds the object's name?

something that does object.create("some_object_name")
Mk 2. (Guest)
on 2009-05-25 21:21
What's the difference between that and

somename = ObjectClass.new
Ben L. (Guest)
on 2009-05-25 21:23
(Received via mailing list)
On Mon, May 25, 2009 at 5:58 PM, Ken T. <removed_email_address@domain.invalid> 
wrote:

> sorry if i've missed something obvious
>
> is there a way in ruby to dynamically create an object from a variable
> that holds the object's name?
>
> something that does object.create("some_object_name")
>

Try:

Kernel.const_get("some_object_name")
Tim H. (Guest)
on 2009-05-25 21:24
(Received via mailing list)
Ken T. wrote:
> sorry if i've missed something obvious
>
> is there a way in ruby to dynamically create an object from a variable
> that holds the object's name?
>
> something that does object.create("some_object_name")

Assuming you mean "a variable that holds the class's name", check out
Module.const_get. This method takes a string and returns the value of
the constant having that name. Since the value of the constant Array is
the Array class object, we can get the Array class object like this:

cls = Module.const_get("Array")

And then call new on the class object to create a new array:

ary = cls.new
Brian C. (Guest)
on 2009-05-25 21:26
Ken T. wrote:
> sorry if i've missed something obvious
>
> is there a way in ruby to dynamically create an object from a variable
> that holds the object's name?

That doesn't make sense - if the object has a name then surely it
already exists?

Perhaps you wish to create an object where a variable holds the name of
the *class* you wish to create a new instance of. In that case:

  klassname = "String"
  klass = Object.const_get(klassname)
  foo = klass.new

If the class name contains :: scope separator, then you need to split on
that first.

  klass = klassname.split('::').inject(Object) { |base,item|
    base.const_get(item)
  }
Ken T. (Guest)
on 2009-05-25 21:37
thanks for all the responses

i'm just learning ruby so sometimes i don't know which end of the
screwdriver to grab
Robert K. (Guest)
on 2009-05-25 23:47
(Received via mailing list)
On 25.05.2009 19:37, Ken T. wrote:
> thanks for all the responses
>
> i'm just learning ruby so sometimes i don't know which end of the
> screwdriver to grab

Hint: if it hurts you got the wrong end. ;-)

Kind regards

  robert
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