End of Life Ruby 3.1 has reached end of life and gets no more fixes. Switch to Ruby 4.0 →
instance method
Object#dup
obj.dup → an_object
object.c
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VALUE
rb_obj_dup(VALUE obj)
{
VALUE dup;
if (special_object_p(obj)) {
return obj;
}
dup = rb_obj_alloc(rb_obj_class(obj));
init_copy(dup, obj);
rb_funcall(dup, id_init_dup, 1, obj);
return dup;
}
Produces a shallow copy of obj—the instance variables of obj are copied, but not the objects they reference.
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.
Example
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:0x401be280> s2.foo #=> "foo" s3 = s1.dup #=> #<Klass:0x401c1084> s3.foo #=> NoMethodError: undefined method `foo' for #<Klass:0x401c1084>