Dynamic Class Initialization

ruby-talk
1

Hi all,
I know this can be done, but I can't find out how to do it. I have a
string with the name of the class that I want to initialize, but how do
I do it?

This is what I tried,

class = "Product"
product = class.new

Obviously this does not work or I wouldn't be asking :slight_smile: So, how do I do
this?

Peer

路路路

--
Posted via http://www.ruby-forum.com/.

2

Hi Peer,

路路路

On Friday, June 15, 2007, at 04:36PM, "Peer Allan" <peer@canadadrugs.com> wrote:

Hi all,
I know this can be done, but I can't find out how to do it. I have a
string with the name of the class that I want to initialize, but how do
I do it?

This is what I tried,

class = "Product"
product = class.new

Obviously this does not work or I wouldn't be asking :slight_smile: So, how do I do
this?

Peer

Try this:

clazz = Object.const_get("Product")
product = clazz.new

The word class is a reserved word so yu should use something different...

Cheers,

Enrique

3

class = "Product"
product = Object.const_get(class).new

Farrel

路路路

On 15/06/07, Peer Allan <peer@canadadrugs.com> wrote:

class = "Product"
product = class.new

4

Peer Allan schrieb:

Hi all,
I know this can be done, but I can't find out how to do it. I have a
string with the name of the class that I want to initialize, but how do
I do it?

This is what I tried,

class = "Product"
product = class.new

Obviously this does not work or I wouldn't be asking :slight_smile: So, how do I do
this?

Peer

I suggest you use this method (out of Rails):

def constantize(camel_cased_word)
   unless /^(::)?([A-Z]\w*)(::[A-Z]\w*)*$/ =~ camel_cased_word
     raise NameError, "#{camel_cased_word.inspect} is not a valid constant name!"
   end

   camel_cased_word = "::#{camel_cased_word}" unless $1
   Object.module_eval(camel_cased_word, __FILE__, __LINE__)
end

It's a bit more powerful than the built-in Ruby Version.

5

Peer Allan wrote:

Hi all,
I know this can be done, but I can't find out how to do it. I have a
string with the name of the class that I want to initialize, but how do
I do it?

This is what I tried,

class = "Product"
product = class.new

Obviously this does not work or I wouldn't be asking :slight_smile: So, how do I do
this?

Peer

hello,may this can work :slight_smile:

product=eval("Product").new

路路路

--
Posted via http://www.ruby-forum.com/\.

6

Thanks all. I knew this couldn't be that difficult. I must have been
searching for the wrong thing.

Peer

路路路

--
Posted via http://www.ruby-forum.com/.

7

Hi Peer,

Hi all,
I know this can be done, but I can't find out how to do it. I have a
string with the name of the class that I want to initialize, but how do
I do it?

This is what I tried,

class = "Product"
product = class.new

Obviously this does not work or I wouldn't be asking :slight_smile: So, how do I do
this?

Peer

Try this:

clazz = Object.const_get("Product")
product = clazz.new

The word class is a reserved word so yu should use something different...

Cheers,

Enrique

   # from Jim Weirich (based on email correspondence)
   def constantize(camel_cased_word)
     camel_cased_word.
       sub(/^::/,'').
       split("::").
       inject(Object) { |scope, name| scope.const_get(name) }
   end

Actually, Jim answered this question twice, once directly and once in a post to our local users group with nearly identical code, but clearly typed in ad hoc both times.

If you need to deal with something like ActiveRecord::Base, the simple form doesn't work:

>> Object.const_get "ActiveRecord::Base"
NameError: wrong constant name ActiveRecord::Base
         from (irb):1:in `const_get'
         from (irb):1
>> "ActiveRecord::Base".split('::').inject(Object) {|scope,name| scope.const_get(name)}
=> ActiveRecord::Base

-Rob

Rob Biedenharn http://agileconsultingllc.com
Rob@AgileConsultingLLC.com

路路路

On Jun 15, 2007, at 10:41 AM, Enrique Comba Riepenhausen wrote:

On Friday, June 15, 2007, at 04:36PM, "Peer Allan" > <peer@canadadrugs.com> wrote:

8

I suggest you use this method (out of Rails):

I suggest you don't. It is more wrong than right. Example:

% irb
>> x =
=>
>> ObjectSpace.each_object(Module) { |k| x << k if k.name =~ /^[a-z]/ }
=> 341
>> x
=> [fatal]

Using module_eval is dumb too. Use this instead:

full_name.split(/::/).inject(Object) { |klass, name| klass.const_get name }

路路路

On Jun 15, 2007, at 08:15 , Daniel Kempkens wrote:

9

Ryan Davis schrieb:

I suggest you use this method (out of Rails):

I suggest you don't. It is more wrong than right. Example:

% irb
>> x =
=>
>> ObjectSpace.each_object(Module) { |k| x << k if k.name =~ /^[a-z]/ }
=> 341
>> x
=> [fatal]

Using module_eval is dumb too. Use this instead:

full_name.split(/::/).inject(Object) { |klass, name| klass.const_get name }

Wow, okay. I didn't know about that.
It's never too late to learn something new :slight_smile:

路路路

On Jun 15, 2007, at 08:15 , Daniel Kempkens wrote: