How to instantiate class from name string in Rails?

klass = Object.const_get "ClassName"

about class methods

class KlassExample
    def self.klass_method
        puts "Hello World from Class method"
    end
end
klass = Object.const_get "KlassExample"
klass.klass_method

irb(main):061:0> klass.klass_method
Hello World from Class method

Others may also be looking for an alternative that does not throw an error if it fails to find the class. safe_constantize is just that.

class MyClass
end

"my_class".classify.safe_constantize.new #  #<MyClass:0x007fec3a96b8a0>
"omg_evil".classify.safe_constantize.new #  nil 

You can simply convert a string and initialize a class out of it by:

klass_name = "Module::ClassName"
klass_name.constantize

To initialize a new object:

klass_name.constantize.new

I hope this turns out to be helpful. Thanks!

I'm surprised nobody is considering security and hacking in their responses. Instantiation of an arbitrary string that likely came even indirectly from user input is asking for trouble and hacking. We all should/must be whitelisting unless we're sure the string is fully controlled and monitored

def class_for(name)
  {
    "foo" => Foo,
    "bar" => Bar,
  }[name] || raise UnknownClass
end

class_for(name_wherever_this_came_from).create!(params_somehow)

How you would know the appropriate params arbitrarily without having a whitelist would be challenging but you get the idea.