Enumerate the Types in Ruby
Ruby is a pure object-oriented language, meaning that all types in Ruby are classes, and each value in a Ruby program is an instance of a class. This has numerous consequences for the way values can be manipulated that may seem odd to programmers familiar with languages that have values which aren't objects. For instance, values in Ruby respond to method calls: The expressions 142.even? and "Hello".empty? are perfectly legitimate (first expression is true and the second is false).
Ruby has many built-in types because it has many built-in classes. Here we only consider a few Ruby types to illustrate how they realize ADTs.