Ruby symbol to class

Question

Is there a way in Ruby to take a symbol or string and turn it into a class of the same name?

For instance, if I have a class such as

class Bob
  def talk
     puts "Hi, I'm bob"
  end
end

And a method I have somewhere else in the code is passed a symbol :bob, can I in some way turn that into the class Bob? Maybe something like

b = :Bob.new
b.talk

Or is there a way to do something similar to this?

Solution 1

There are many ways to do this. Your lack of context makes it impossible to elect a "best" way. Here's a few ayways.

Kernel.const_get(:Bob)

eval(:Bob.to_s)

Kernel.const_get(:bob.to_s.capitalize)

Solution 2

Rails

For use with Rails only.

With a string:

"Module".constantize #=> Module
"Class".constantize #=> Class

With a symbol:

:module.to_s.classify.constantize #=> Module
:open_struct.to_s.classify.constantize #=> OpenStruct

If you are dealing with a multi-word symbol, then you'll want to add #classify to the chain to properly handle the capitalization of all the parts of the constant.

http://api.rubyonrails.org/classes/ActiveSupport/Inflector.html#method-i-constantize

Solution 3

None of the solutions I've seen work if you want to turn :foo_bar into FooBar. If that's what you're looking for:

:foo_bar.to_s.split("_").collect(&:capitalize).join.constantize
=> FooBar

hope that helps someone.

Solution 4

NameSpace.const_get(classname) will return the class object (assuming that classname contains the name of a class - if it contains the name of a constant that is not a class, it will return the value of that constant). The toplevel namespace is Object, so you can do Object.const_get(:Bob).new

Solution 5

class Bob
end

def create(name)
  return eval("#{name}.new")
end

b = create(:Bob)
puts b.class

View more solutions

Comments

[intargc]

Well, thankfully I didn't ask for the "best" way, but just a way... ;)

[Dave Sims]

That's what 'camelize' is for: :foo_bar.to_s.camelize

[Ross Allen]

@DaveSims camelize is an ActiveRecord extension: api.rubyonrails.org/classes/ActiveSupport/…, although so is constantize.

[Dave Sims]

Yes, like Dan Frade, I should have mentioned that. :)

[JustinStolle]

Are you asking a question inside of an answer? For shame! ;)

[Joe]

@JustinStolle, I don't think its a new question, more guidance regarding to the original question? :)

[phil pirozhkov]

just for the case, if Bob is defined in module People and you know it, you can People.const_get(:Bob)

[superluminary]

If you're using Rails this is probably the best solution.

[tjbp]

The question specifically asks about symbols and constantize does not exist on the Symbol class in Rails. Answer should be :Module.to_s.constantize.