Question

I am building a gem which will append a particular string to every puts output. A use case might look like this:

string_to_append = " hello world!"
puts "The web server is running on port 80"
# => The web server is running on port 80 hello world!

I am not sure how to do this. A pseudo-code of it might be something like this:

class GemName
  def append
    until 2 < 1
        if puts_is_used == true
            puts string << "hello world!"
        else
            puts ""
        end
    end
  end
end

Any insight into the best approach regarding how to do this is very much appreciated.

Answer 1

This can easily be done with aliasing. I’d say that this is a very common idiom for decorating methods.

# "open" Kernel module, that's where the `puts` lives.
module Kernel
  # our new puts
  def puts_with_append *args
    new_args = args.map{|a| a + ' hello world'}
    puts_without_append *new_args
  end

  # back up name of old puts
  alias_method :puts_without_append, :puts

  # now set our version as new puts
  alias_method :puts, :puts_with_append
end

puts 'foo'
# >> foo hello world

# it works with multiple parameters correctly
puts 'bar', 'quux'
# >> bar hello world
# >> quux hello world