Dynamic Class Initialization

[Peer Allan]

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 So, how do I do
this?

Peer

 

[Enrique Comba Riepenhausen]

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 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

 

[Farrel Lifson]

class = "Product"
product = class.new

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

Farrel

 

[Peer Allan]

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

Peer

 

[Daniel Kempkens]

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 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.

 

[Rob Biedenharn]

Hi 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:
NameError: wrong constant name ActiveRecord::Base
from (irb):1:in `const_get'
from (irb):1scope.const_get(name)}
=> ActiveRecord::Base

-Rob


Rob Biedenharn http://agileconsultingllc.com
(e-mail address removed)

 

[gz zz]

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 So, how do I do
this?

Peer

hello,may this can work

product=eval("Product").new

 

[Ryan Davis]

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 }

 

[Daniel Kempkens]

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