eql.rb

RUBY_VERSION                    # => "2.7.0"

"a".hash                        # => -4127323257193555845
"b".hash                        # => -2092951289148142958
"foo".hash                      # => -4298047480057265190
"bar".hash                      # => 4242949873151017721

h = {"foo" => 0}

h["foo"]                        # => 0
h["bar"]                        # => nil

class String
  alias_method("original_hash", "hash")

  def hash
    case self
    when "foo" then -1
    when "bar" then -1
    else original_hash
    end
  end
end

"a".hash                        # => -4127323257193555845
"b".hash                        # => -2092951289148142958
"foo".hash                      # => -1
"bar".hash                      # => -1

"foo".hash == "bar".hash        # => true

h = {"foo" => 0}

h["foo"]                        # => 0
h["bar"]                        # => nil

"foo".eql? "foo"                # => true
"foo".eql? "bar"                # => false
"bar".eql? "foo"                # => false
"bar".eql? "bar"                # => true