Source: Class: Object [ruby-doc.org]
Returns an array representation of obj. For objects of class Object and others that don‘t explicitly override the method, the return value is an array containing self. However, this latter behavior will soon be obsolete.
self.to_a #=> -:1: warning: default `to_a' will be obsolete
"hello".to_a #=> ["hello"]
Time.new.to_a #=> [39, 54, 8, 9, 4, 2003, 3, 99, true, "CDT"]