ruby exception extending tricks

test_exception_extending.rb

# we can extend exception with arbitrary modules, add metadata and so on
# we can then rescue from that module!

module MyAttr
  attr_accessor :my_attr
end

class MyException < StandardError
end

def foo
  raise MyException, "messsage"
rescue MyException => e
  e.extend MyAttr
  e.my_attr = "hahaha it works!"
  raise
end

begin
  foo
rescue MyAttr => e
  puts e.message
  puts e.my_attr
  puts e.class
  puts e.backtrace
end

# result:

# messsage
# hahaha it works!
# MyException
# test_exception_extending.rb:12:in `foo'
# test_exception_extending.rb:20:in `<main>'