autoreloading of ruby files which have changed in the meantime

autoreload.rb

# This file extends the Kernel's require function and adds the 
# AutoReload module which allows to reload files once they have changed
# on the disk.
#
# Basically, you just require your files as usual, and if you want to update
# the files, either call AutoReload.reload(file) or AutoReload.reload_all.
#
# Usage:
#   irb -rautoload
#
# Then type 'reload' on the prompt to reload require'd files which have
# changed in the meantime.
#
# Written by Mikio L. Braun, March 16, 2008, edited Jan 15, 2010

require 'pp'
require 'set'

# This module tracks loaded files and their timestamps and allows to reload
# files which have changed automatically by calling reload.
module AutoReload
  # stores the normalized filenames and their File.mtime timestamps
  @timestamps = Hash.new
  @notfound = Set.new
  @verbose = false
  
  def self.verbose=(flag)
    @verbose = flag
  end
  
  # find the full path to a file
  def self.locate(file)
    return nil if @notfound.include? file
    $:.each do |dir|
      fullpath = File.join(dir, file)
      if File.exists? fullpath
        return fullpath
      elsif File.exists?(fullpath + '.rb')
        return fullpath + '.rb'
      elsif File.exists?(fullpath + '.so')
        return fullpath + '.so'
      end
    end
    # puts "[AutoReload] File #{file} not found!"
    @notfound.add file
    return nil
  end
  
  # store the time stamp of a file
  def self.timestamp(file)
    path = locate(file)
    if path
      file = normalize(path, file)
      @timestamps[file] = File.mtime(path)
    end
  end
  
  # put the extension on a filename
  def self.normalize(path, file)
    if File.extname(file) == ""
      return file + File.extname(path)
    else
      return file
    end
  end
  
  # show all stored files and their timestamp
  def self.dump
    pp @timestamps
  end
  
  # reload a file
  def self.reload(file, force=false)
    path = locate(file)
    file = normalize(path, file)
    
    if force or (path and File.mtime(path) > @timestamps[file])
      puts "[AutoReload] reloading #{file}" if @verbose
      
      # delete file from list of loaded modules, and reload
      $".delete file
      require file
      return true
    else
      return false
    end
  end
  
  # reload all files which were required
  def self.reload_all(force=false)
    @timestamps.each_key do |file|
      self.reload(file, force)
    end
  end
end

# Overwrite 'require' to register the time stamps instead.
module Kernel # :nodoc:
  alias old_require require
  
  def require(file)
    AutoReload.timestamp(file)
    old_require(file)
  end

  def reload
    AutoReload.reload_all
    return
  end
end