Ruby - raise and rescue

General syntax

begin
  ...
rescue TooHotError => too_hot
  # This code is run if a TooHotError occurs 
rescue TooColdError => too_cold
  # This code is run if a TooColdError occurs 
else
  # This code is run if no exception occurred at all
ensure
  # This code is always run, regardless of whether an exception occurred
end

Multiple rescues

Second rescue’s exception class also covers first rescue’s exception class

• The first rescue block will run

class TimeoutError < StandardError; end;
 
begin
	raise TimeoutError
rescue TimeoutError
	puts "Inside the first rescue"
rescue StandardError
	puts "Inside the second rescue"
end
 
#=> Inside the first rescue

The retry keyword

• Ruby provides the retry keyword to retry the code inside the begin..end block

counter = 0
begin
  counter += 1
  make_api_request
rescue
  retry if counter <= 3  
end

Reraising exceptions

• Calling raise with no arguments inside the rescue block will re-raise the original rescued exception
• The re-raised exception cannot be distinguished from the original exception

begin
  ...
rescue => e
  raise if e.message == "Fubar"
end
 
# Will re-raise the exception that was rescued if the message of the exception is "Fubar"

Advanced topics

• How does rescue matchers work in Ruby and how can we hack it
• Ruby - Multiple ways to raise exceptions

Sources

• https://www.exceptionalcreatures.com/guides/advanced-rescue-and-raise