But unfortunately I have to call two such functions in chain and both
have a block as parameter, so eval would be my last choice. So I'm
looking for a way to call the function like I could call them if it
would be an Object Method:
Class.get_objet_by_name("ClassName").send(:name)

any suggestions?

   str = String.new("ruby")
   obj_name = "str"
   eval(obj_name).send("length")
   => 4

Would something like this work?

So am I'm right that eval("Classname") returns some kind of "default
initialized" Object of type Classname?

         Math.const_get(:PI)   #=> 3.14159265358979

Is a class name treated like a constant in ruyb? Or is my documentation
not up to date? Or is it just an undocumented feature?

   Foo = Class.new{}
   Bar = Module.new{}

If you want to make sure the object returned by Module#const_get is a
class, you can just test its class:

   class Module
     def class_get(name)
       cl = const_get(name)
       unless cl.kind_of? Class
         raise TypeError, "`#{cl.inspect}' must be a Class"
       end
       return cl
     end
   end

of course, you could also just accept all objects that respond to #new,
which would be quackier:

   class Module
     def class_get(name)
       cl = const_get(name)
       unless cl.respond_to? :new
         raise TypeError, "`#{cl.inspect}' must respond to `new'"
       end
       return cl
     end
   end