class Symbol: A +Symbol+ object represents a named identifier inside the Ruby interpreter. literals.| docs.ruby-lang.org
class String: A +String+ object has an arbitrary sequence of bytes, typically representing text or binary data. new or as literals.| docs.ruby-lang.org
class Proc: A +Proc+ object is an encapsulation of a block of code, which can be stored in a local variable, passed to a method or another Proc, and can be called| docs.ruby-lang.org