map_module_method_to_proc.rb

module Email
  def self.get_domain(email_address)
    email_address&.split('@')&.last
  end
end

emails = [ 'brad@these8bits.com' ]

p emails.map(&Email.method(:get_domain))

# $ ruby ex.rb
# ["these8bits.com"]

map_module_method_to_proc1.rb

class Proc
  # "f after g"
  def <<(g)
    f = self
    Proc.new {|x| f.(g.(x))}
  end
end

module Email
  def self.get_domain(email_address)
    email_address&.split('@')&.last
  end
end

User = Struct.new :email
users = [ User.new('brad@these8bits.com') ]

p users.map(&(Email.method(:get_domain).to_proc << :email.to_proc))
# => ["these8bits.com"]