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I've probably overlooked something, and hopefully someone can help me
out. I want to be able to create arbitrary object from the contents of a
string.

For example, if I had the following string:

classname = "Array"

How can I create an Array object, knowing only that the variable
classname held the name of some class as a string.

On Apr 29, 2005, at 12:38 PM, Matthew Thill wrote:

> I've probably overlooked something, and hopefully someone can help me
> out. I want to be able to create arbitrary object from the contents of
> a string.
>
> For example, if I had the following string:
>
> classname = "Array"
>
> How can I create an Array object, knowing only that the variable
> classname held the name of some class as a string.

You're looking for Object.const_get():

irb(main):003:0> class_obj = Object.const_get("Array")
=> Array
irb(main):004:0> arr = class_obj.new
=> []

Hope that helps.

James Edward Gray II

Yes, that is exactly what I wanted. Thank you.

James Edward Gray II wrote:
> On Apr 29, 2005, at 12:38 PM, Matthew Thill wrote:
>
>> I've probably overlooked something, and hopefully someone can help me
>> out. I want to be able to create arbitrary object from the contents of
>> a string.
>>
>> For example, if I had the following string:
>>
>> classname = "Array"
>>
>> How can I create an Array object, knowing only that the variable
>> classname held the name of some class as a string.
>
>
> You're looking for Object.const_get():
>
> irb(main):003:0> class_obj = Object.const_get("Array")
> => Array
> irb(main):004:0> arr = class_obj.new
> => []
>
> Hope that helps.
>
> James Edward Gray II
>
>

On 4/29/05, James Edward Gray II <> wrote:
> On Apr 29, 2005, at 12:38 PM, Matthew Thill wrote:
>
> > I've probably overlooked something, and hopefully someone can help me
> > out. I want to be able to create arbitrary object from the contents of
> > a string.
> >
> > For example, if I had the following string:
> >
> > classname = "Array"
> >
> > How can I create an Array object, knowing only that the variable
> > classname held the name of some class as a string.
>
> You're looking for Object.const_get():

Don't you mean Module.const_get()?

On Sat, 2005-04-30 at 03:05 +0900, James Edward Gray II wrote:
> On Apr 29, 2005, at 12:38 PM, Matthew Thill wrote:
>
> > I've probably overlooked something, and hopefully someone can help me
> > out. I want to be able to create arbitrary object from the contents of
> > a string.
> >
> > For example, if I had the following string:
> >
> > classname = "Array"
> >
> > How can I create an Array object, knowing only that the variable
> > classname held the name of some class as a string.
>
> You're looking for Object.const_get():
>
> irb(main):003:0> class_obj = Object.const_get("Array")
> => Array
> irb(main):004:0> arr = class_obj.new
> => []
>
> Hope that helps.
>
> James Edward Gray II
>
>
>

If your class is nested in a module or other class, you might want to do
something like:

irb:0> module A
irb:1> class B
irb:2> class C
irb:3> end
irb:2> end
irb:1> end
=> nil
irb:0> classname = 'A::B::C'
=> "A::B::C"
irb:0> klass = classname.split('::').inject(Class) do |sum, elem|
irb:1* sum.const_get(elem)
irb:1> end
=> A::B::C
irb:0> klass.new
=> #<A::B::C:0xb7d12640>

On Apr 29, 2005, at 1:24 PM, Joe Van Dyk wrote:

> Don't you mean Module.const_get()?

Yes, my bad. Module.const_get() called on Object, is what I meant.

James Edward Gray II

On Sat, 30 Apr 2005, Matthew Thill wrote:

> I've probably overlooked something, and hopefully someone can help me
> out. I want to be able to create arbitrary object from the contents of a
> string.
>
> For example, if I had the following string:
>
> classname = "Array"
>
> How can I create an Array object, knowing only that the variable
> classname held the name of some class as a string.

this is from my utility lib:

harp:~ > cat a.rb
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

module A
module B
module C
class X
class Y
class Z
def initialize(*bits, &block)
n = 0
bits.reverse.each_with_index{|bit, i| n |= (bit << i)}
block.call n
end
end
end
end
end
end
end

klass_stamp('A::B::C::X::Y::Z', 1, 0, 1, 0, 1, 0){ |n| p n }

harp:~ > ruby a.rb
42


HTH.

-a
--
================================================== =============================
| email :: ara [dot] t [dot] howard [at] noaa [dot] gov
| phone :: 303.497.6469
| renunciation is not getting rid of the things of this world, but accepting
| that they pass away. --aitken roshi
================================================== =============================

On 4/29/05, James Edward Gray II <> wrote:
> On Apr 29, 2005, at 1:24 PM, Joe Van Dyk wrote:
>
> > Don't you mean Module.const_get()?
>
> Yes, my bad. Module.const_get() called on Object, is what I meant.

actually, Module#const_get, or Object.const_get, IMHO

Also, the OP might look at #allocate. #allocate never needs arguments,
#new might fail without arguments. Of course, allocate doesn't
initialize...

klass = "Array"
Object.const_get(klass).allocate #==> []

cheers,
Mark

On 29.4.2005, at 22:50, Mark Hubbart wrote:

> Also, the OP might look at #allocate. #allocate never needs arguments,
> #new might fail without arguments. Of course, allocate doesn't
> initialize...
>
> klass = "Array"
> Object.const_get(klass).allocate #==> []
>
> cheers,
> Mark
>

Whoah, how did this escape me for so long!?

#allocate

Awesome, this'll let me abuse classes in a whole new fashion
*cue evil laughter echoing from the depths of a dark forest*

Thanks a million for the insight,
Ilmari

Matthew Thill wrote:
> I've probably overlooked something, and hopefully someone can help me
> out. I want to be able to create arbitrary object from the contents of a
> string.
>
> For example, if I had the following string:
>
> classname = "Array"
>
> How can I create an Array object, knowing only that the variable
> classname held the name of some class as a string.
>

Thanks for the responses everyone. I have plenty of new ideas to work
with now.