dup()
public
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference. dup copies the tainted state of obj.
This method may have class-specific behavior. If so, that behavior will be documented under the #initialize_copy method of the class.
on dup vs clone
In general, clone and dup may have different semantics in descendant classes. While clone is used to duplicate an object, including its internal state, dup typically uses the class of the descendant object to create the new instance.
When using #dup, any modules that the object has been extended with will not be copied.
class Klass attr_accessor :str end module Foo def foo; 'foo'; end end s1 = Klass.new #=> #<Klass:0x401b3a38> s1.extend(Foo) #=> #<Klass:0x401b3a38> s1.foo #=> "foo" s2 = s1.clone #=> #<Klass:0x401b3a38> s2.foo #=> "foo" s3 = s1.dup #=> #<Klass:0x401b3a38> s3.foo #=> NoMethodError: undefined method `foo' for #<Klass:0x401b3a38>
Dup vs Clone difference
As for me main difference between .dup and .clone , that first one doesn’t not freeze result object if initial object was frozen.