Defining operators as if they were ordinary methods using the append (<<) and spaceship operator (<=>) operator

custom_operators.rb

Sample code: Append Operator(<<)
class Inbox

  attr_reader :unread_count
  
  def initialize
    @messages  = []
    @unread_count = 0
  end
  
  def <<(msg)
    @unread_count += 1
    @messages << msg
    return self
  end
end


Sample Usage:
>> i = Inbox.new
=> #<Inbox: @messages=[], @unread_count=0>

>> i << "foo" << "bar"
=> #<Inbox: @messages=["foo", "bar", "baz"], @unread_count=3> 

>> i.unread_count
=> 2

Good habit:
Have your << method return the object itself, so the calls can be chained


Code: Spaceship Operator(<=>)
class Tree
  include Comparable
  
  attr_reader :age
  def initialize(age)
    @age = age
  end
  
  def <=>(other_tree)
    age <=> other_tree.age
  end
end

Usage:
>> a = Tree.new(2)
=> #<Tree:0x5c9ba8 @age=2>

>> b = Tree.new(3)
=> #<Tree:0x5c7fb0 @age=3>

>> c = Tree.new(3)
=> #<Tree:0x5c63b8 @age=3>

>> a < b
=> true

>> b == c
=> true

>> c > a
=> true

>> c != a
=> true