Ruby's rescue exception and retry functionality

retry.rb

def sometimes_fails
  puts "Beginning of sometimes_fails"
  
  begin
    retries ||= 0
    puts "About to do a thing (#{retries})"

    raise StandardError if rand(5) != 4

    puts "Success!"
  rescue StandardError => e
    retry if (retries += 1) < 3

    # all retries failed, re-raise exception
    raise e
  end
end

sometimes_fails

# A run where the retries eventually succeed:
#
# > ruby retry.rb
# Beginning of sometimes_fails
# About to do a thing (0)
# About to do a thing (1)
# About to do a thing (2)
# Success!

# A run where the retries run out:
#
# > ruby retry.rb
# Beginning of sometimes_fails
# About to do a thing (0)
# About to do a thing (1)
# About to do a thing (2)
# Traceback (most recent call last):
#         1: from retry.rb:17:in `<main>'
# retry.rb:6:in `sometimes_fails': StandardError (StandardError)