How to convert a string to a constant in Ruby?

Question

How to convert the string "User" to User?

I would also like an answer to this question; however, are you trying to create a new constant based on a string, OR find an already initialized constant? Also are you looking for vanilla ruby or also Rails? — user3373470
– user3373470, Commented Aug 26, 2015 at 20:37

Damien · Accepted Answer · 2012-09-18 15:15:54Z

108

Object.const_get("User")

No need to require ActiveSupport.

answered Sep 18, 2012 at 15:15

Damien

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1 Comment

Artur INTECH Over a year ago

Usage example: class User; def self.lookup; const_get('SomeClassName);end; end User.lookup will return class itself.

C. K. Young · Accepted Answer · 2010-03-02 06:48:12Z

You can use the Module#const_get method. Example:

irb(main):001:0> ARGV => [] irb(main):002:0> Kernel.const_get "ARGV" => []

severin · Accepted Answer · 2010-03-02 07:23:09Z

38

If you have ActiveSupport loaded (e.g. in Rails) you can use

"User".constantize

answered Mar 2, 2010 at 7:23

severin

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Comments

weakish · Accepted Answer · 2015-04-01 04:45:44Z

The recommended way is to use ActiveSupport's constantize:

'User'.constantize

You can also use Kernel's const_get, but in Ruby < 2.0, it does not support namespaced constants, so something like this:

Kernel.const_get('Foobar::User')

will fail in Ruby < 2.0. So if you want a generic solution, you'd be wise to use the ActiveSupport approach:

def my_constantize(class_name) unless /\A(?:::)?([A-Z]\w*(?:::[A-Z]\w*)*)\z/ =~ class_name raise NameError, "#{class_name.inspect} is not a valid constant name!" end Object.module_eval("::#{$1}", __FILE__, __LINE__) end

Since Ruby 2.0 has reached EOL, there is no longer any need to pull in ActiveSupport as a dependency to reference a constant with a string. :-)

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