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ruby

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# handle IOError
end
# good
def with_io_error_handling
yield
rescue IOError
# handle IOError
end
with_io_error_handling { something_that_might_fail }
with_io_error_handling { something_else_that_might_fail }
----
=== Suppressing Exceptions [[dont-hide-exceptions]]
Don't suppress exceptions.
[source,ruby]
----
# bad
begin
do_something # an exception occurs here
rescue SomeError
end
# good
begin
do_something # an exception occurs here
rescue SomeError
handle_exception
end
# good
begin
do_something # an exception occurs here
rescue SomeError
# Notes on why exception handling is not performed
end
# good
do_something rescue nil
----
=== Using `rescue` as a Modifier [[no-rescue-modifiers]]
Avoid using `rescue` in its modifier form.
[source,ruby]
----
# bad - this catches exceptions of StandardError class and its descendant classes
read_file rescue handle_error($!)
# good - this catches only the exceptions of Errno::ENOENT class and its descendant classes
def foo
read_file
rescue Errno::ENOENT => e
handle_error(e)
end
----
=== Using Exceptions for Flow of Control [[no-exceptional-flows]]
Don't use exceptions for flow of control.
[source,ruby]
----
# bad
begin
n / d
rescue ZeroDivisionError
puts 'Cannot divide by 0!'
end
# good
if d.zero?
puts 'Cannot divide by 0!'
else
n / d
end
----
=== Blind Rescues [[no-blind-rescues]]
Avoid rescuing the `Exception` class.
This will trap signals and calls to `exit`, requiring you to `kill -9` the process.
[source,ruby]
----
# bad
begin
# calls to exit and kill signals will be caught (except kill -9)
exit
rescue Exception
puts "you didn't really want to exit, right?"
# exception handling
end
# good