Question

I was hacking a to_hash to Object (I’m not saying this is a good idea, just an experiment). When I came across an odd issue, where IO stopped working.

#lib/object.rb
class Object
  def to_hash
    self.instance_variables.inject({}) { |hash,var| hash[var.to_s.delete("@")] = self.instance_variable_get(var); hash } 
  end
end

#run_test1.rb
require_relative 'lib/Object'
require 'FileUtils'

puts 'run test'


#run_test2.rb
require_relative 'lib/Object'

File.open('test.txt', 'w') {|f| f.write('this is a test')}

in run_test1 I get an

<internal:lib/rubygems/custom_require>:29:in `set_encoding': wrong number of arguments (0 for 1..2) (ArgumentError)
        from <internal:lib/rubygems/custom_require>:29:in `require'
        from <internal:lib/rubygems/custom_require>:29:in `require'
        from .../run_test1.rb:2:in `<main>'

in run_test2 I get

run_test2.rb:3:in `initialize': No such file or directory - test.txt (Errno::ENOENT
        from run_test2.rb:3:in `open'
        from run_test2.rb:3:in `<main>'

(if the file exists it says the file is not open for writing)

While I’m not surprised it happened – just curious, What is going on here? Theoretically it should be fine, however what is the underlying cause.

The relevant info:

• ruby 1.9.2p290 (2011-07-09) [i386-mingw32]
• XP SP3 32-bit
• RUBYGEMS VERSION: 1.8.12

Answer 1

The to_hash method is used to identify objects that coerce to Hash. In that sense, it behaves like to_ary or to_str. The method you implemented is more like to_a or to_s.

Lots of Ruby code, including Ruby core code, checks for to_hash to figure out whether an argument is an options hash (arg.respond_to? :to_hash) and from there on follow a different execution path. This gets even more messed up by some code checking if the object is a real hash or not (Hash === arg).

You might want to name your method to_h or something similar.