public_send calls a method whose name is only data.

Metaprogramming is code that works with code: calling, creating or catching methods while the program runs. The first tool is send. order.send(:total) does the same as order.total, but the method name is a symbol or string you can keep in a variable, read from a file or build from text.

send can even call private methods, which is rarely what you want. public_send refuses, so professionals prefer it for names that come from outside. Before calling, respond_to? asks whether the object has that method at all, so one bad name in the data does not crash the whole report.

class Order
  attr_accessor :total, :status
end
order = Order.new
order.total = 42
order.status = "packed"
["total", "status", "colour"].each do |column|
  if order.respond_to?(column)
    puts "#{column}: #{order.public_send(column)}"
  else
    puts "#{column}: no such column"
  end
end

Never pass a name typed by a stranger straight to send, because it could call almost anything.