Which exception classes does "rescue" trap?

ruby-talk
1

Hi, using Ruby 1.9 I've realized that "rescue" traps more than
StandardError exceptions, for example NoMemoryError:

NoMemoryError.ancestors

[NoMemoryError, Exception, Object, PP::ObjectMixin, Kernel, BasicObject]

begin
  raise NoMemoryError, "NO MEMORY !!!"
rescue
  puts "rescued"
end

=> rescued

But for example it does not trap ScriptError exceptions. So which
exact exception classes does "rescue" trap? is it docummented
somewhere? Unfortunately I am not able to find in Ruby sources where
the definition of "rescue" is.

Thanks a lot.

···

--
Iñaki Baz Castillo
<ibc@aliax.net>

2

Hi, using Ruby 1.9 I've realized that "rescue" traps more than
StandardError exceptions, for example NoMemoryError:

Not for me it doesn't.

irb
1.9.3p125 :001 > NoMemoryError.ancestors
=> [NoMemoryError, Exception, Object, Kernel, BasicObject]
1.9.3p125 :002 >
1.9.3p125 :003 > begin
1.9.3p125 :004 > raise NoMemoryError, "NO MEMORY !!!"
1.9.3p125 :005?> rescue
1.9.3p125 :006?> puts "rescued"
1.9.3p125 :007?> end
NoMemoryError: NO MEMORY !!!
  from (irb):4
  from /Users/henry/.rvm/rubies/ruby-1.9.3-p125/bin/irb:16:in `<main>'
1.9.3p125 :008 >

But for example it does not trap ScriptError exceptions. So which
exact exception classes does "rescue" trap? is it docummented
somewhere? Unfortunately I am not able to find in Ruby sources where
the definition of "rescue" is.

Google is your friend...

http://jpablobr.com/past/ruby-s-exception-hierarchy

Rescuing an Exception class will also rescue it's sub-classes. This doesn't work work for modules though, which would be really handy.

Henry

···

On 17/05/2012, at 9:59 AM, Iñaki Baz Castillo wrote:

3

Hi,

SignalExceptions are *not* rescued. You probably used a wrong argument
for the signal and caused an ArgumentError, which is then rescued:

begin
  raise SignalException, 'foo'
rescue => error
  p "#{error.class}: #{error.message}" # error is *not* a
SignalException
end

···

--
Posted via http://www.ruby-forum.com/.

4

According to the "IPA Ruby Standardization WG Draft August 25, 2010"

(page 97)
11.5.2.5 The begin expression
  Semantics
  c.2
"If the exception-class-list is omitted in the rescue-clause, and if E
is an instance of the class StandardError, the rescue-clause handles E."

If any Ruby interpreter handles any exception that is not a sub-class of
StandardError in a rescue-clause (no exception-class-list), then it is
in error.

···

--
Posted via http://www.ruby-forum.com/.

5

Hi, using Ruby 1.9 I've realized that "rescue" traps more than
StandardError exceptions, for example NoMemoryError:

Not for me it doesn't.

My fault, sorry, I did a wrong code.

But for example it does not trap ScriptError exceptions. So which
exact exception classes does "rescue" trap? is it docummented
somewhere? Unfortunately I am not able to find in Ruby sources where
the definition of "rescue" is.

Google is your friend...

http://jpablobr.com/past/ruby-s-exception-hierarchy

Rescuing an Exception class will also rescue it's sub-classes. This doesn't work work for modules though, which would be really handy.

Yes sure :slight_smile:

My question is, however: does "rescue" trap any exception class not
inheriting from StandardError?

But don't worry, I'm coding some script right now to discover it :slight_smile:

Thanks a lot.

···

2012/5/17 Henry Maddocks <hmaddocks@me.com>:

On 17/05/2012, at 9:59 AM, Iñaki Baz Castillo wrote:

--
Iñaki Baz Castillo
<ibc@aliax.net>

6

Correct. That makes more sense.

Henry

···

On 17/05/2012, at 12:02 PM, Jan E. wrote:

Hi,

SignalExceptions are *not* rescued. You probably used a wrong argument
for the signal and caused an ArgumentError, which is then rescued:

7

You are right:

begin
  raise SignalException
rescue => e
  puts "Exception #{e.inspect} rescued"
end

Output:

Exception #<ArgumentError: wrong number of arguments (0 for 1)> rescued

It seems that SingalException.new requires one argument.

Thanks a lot.

···

2012/5/17 Jan E. <lists@ruby-forum.com>:

SignalExceptions are *not* rescued. You probably used a wrong argument
for the signal and caused an ArgumentError, which is then rescued:

--
Iñaki Baz Castillo
<ibc@aliax.net>

8

Clear and confirmed now. Thanks a lot.

···

2012/5/17 Llelan D. <lists@ruby-forum.com>:

According to the "IPA Ruby Standardization WG Draft August 25, 2010"

(page 97)
11.5.2.5 The begin expression
Semantics
c.2
"If the exception-class-list is omitted in the rescue-clause, and if E
is an instance of the class StandardError, the rescue-clause handles E."

If any Ruby interpreter handles any exception that is not a sub-class of
StandardError in a rescue-clause (no exception-class-list), then it is
in error.

--
Iñaki Baz Castillo
<ibc@aliax.net>

9

Code done. If I'm not wrong, "rescue" traps the following exception
classes (and of course all the sub-classes):

- SignalException
- StandardError

···

2012/5/17 Iñaki Baz Castillo <ibc@aliax.net>:

My question is, however: does "rescue" trap any exception class not
inheriting from StandardError?

--
Iñaki Baz Castillo
<ibc@aliax.net>

10

Here's one prepared earlier

http://blog.nicksieger.com/articles/2006/09/06/rubys-exception-hierarchy

Henry

···

On 17/05/2012, at 10:45 AM, Iñaki Baz Castillo wrote:

But don't worry, I'm coding some script right now to discover it :slight_smile:

11

So it does. That's unexpected.

Henry

···

On 17/05/2012, at 10:56 AM, Iñaki Baz Castillo wrote:

2012/5/17 Iñaki Baz Castillo <ibc@aliax.net>:

My question is, however: does "rescue" trap any exception class not
inheriting from StandardError?

Code done. If I'm not wrong, "rescue" traps the following exception
classes (and of course all the sub-classes):

- SignalException
- StandardError