Forum: Ruby OptionParser and Exceptions

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Srijayanth S. (Guest)
on 2009-04-15 15:47
(Received via mailing list)
Hello,

The following code:

require 'optparse'

optparser = OptionParser.new do |args|
        list=[:foo,:bar,:baz]
        begin
                args.on("--l [OPTION]",list,"Blah") { |o| }
        rescue
                puts "Rescuing in the block"
        end
end

begin
        optparser.parse!(ARGV)
rescue
        puts "Rescuing in main"
end

./foo.rb -l FOO ends up being rescued in main.

Why is this? the parse! method just calls the block defined in new
doesn't
it? In which case, a begin and rescue block should work there right?
Even if
I remove the begin and rescue block in main, it doesn't get rescued at
all,
it just ends up spitting the usual ugly error etc.

I am currently on Ruby 1.8.6.

Thanks,

Jayanth
Jan F. (Guest)
on 2009-04-15 16:01
(Received via mailing list)
Srijayanth S. <removed_email_address@domain.invalid> wrote:
> Why is this? the parse! method just calls the block defined in new
> doesn't it?
No it doesn't:

require 'optparse'

optparser = OptionParser.new do |args|
  puts 'Here in OptionParser.new'
end

puts 'Before optparser.parse!'
optparser.parse!
puts 'After  optparser.parse!'

Regards,
Jan
Robert K. (Guest)
on 2009-04-15 16:06
(Received via mailing list)
2009/4/15 Srijayanth S. <removed_email_address@domain.invalid>:
>        rescue
>                puts "Rescuing in the block"
>        end

This rescue does not make sense.  Because the code is invoked once
upon OptionParser.new.  Parsing errors are thrown from parse and
parse!.

> Why is this? the parse! method just calls the block defined in new doesn't
> it? In which case, a begin and rescue block should work there right? Even if
> I remove the begin and rescue block in main, it doesn't get rescued at all,
> it just ends up spitting the usual ugly error etc.

You need to rescue Exception because rescue without any arguments only
rescues RuntimeErrors IIRC, it definitively does not catch every sub
class of Exception.

Cheers

robert
Srijayanth S. (Guest)
on 2009-04-15 16:15
(Received via mailing list)
Thanks both of you.

Jayanth

On Wed, Apr 15, 2009 at 5:35 PM, Robert K.
Brian C. (Guest)
on 2009-04-15 16:58
Robert K. wrote:
> You need to rescue Exception because rescue without any arguments only
> rescues RuntimeErrors IIRC

rescue without any arguments rescues StandardError. (StandardError is an
ancestor of RuntimeError, and Exception is an ancestor of StandardError)

See:
http://www.zenspider.com/Languages/Ruby/QuickRef.html#34

You should normally be a bit wary of 'rescue Exception'. This will
rescue all sorts of internal failures like NoMemoryError or SyntaxError
which you may not want to hide.
Robert K. (Guest)
on 2009-04-15 17:12
(Received via mailing list)
2009/4/15 Brian C. <removed_email_address@domain.invalid>:
> Robert K. wrote:
>> You need to rescue Exception because rescue without any arguments only
>> rescues RuntimeErrors IIRC
>
> rescue without any arguments rescues StandardError. (StandardError is an
> ancestor of RuntimeError, and Exception is an ancestor of StandardError)

Thank you for the correction!

robert
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