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comp.lang.ruby

OptionParser and Exceptions

Srijayanth Sridhar

4/15/2009 11:47:00 AM

[Note: parts of this message were removed to make it a legal post.]

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
5 Answers

Jan Friedrich

4/15/2009 11:58:00 AM

0

Srijayanth Sridhar <srijayanth@gmail.com> 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 Klemme

4/15/2009 12:06:00 PM

0

2009/4/15 Srijayanth Sridhar <srijayanth@gmail.com>:
> Hello,
>
> The following code:
>
> require 'optparse'
>
> optparser =3D OptionParser.new do |args|
> =A0 =A0 =A0 =A0list=3D[:foo,:bar,:baz]
> =A0 =A0 =A0 =A0begin
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0args.on("--l [OPTION]",list,"Blah") { |o| =
}
> =A0 =A0 =A0 =A0rescue
> =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0puts "Rescuing in the block"
> =A0 =A0 =A0 =A0end

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

> end
>
> begin
> =A0 =A0 =A0 =A0optparser.parse!(ARGV)
> rescue
> =A0 =A0 =A0 =A0puts "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 al=
l,
> 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

--=20
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestprac...

Srijayanth Sridhar

4/15/2009 12:15:00 PM

0

[Note: parts of this message were removed to make it a legal post.]

Thanks both of you.

Jayanth

On Wed, Apr 15, 2009 at 5:35 PM, Robert Klemme
<shortcutter@googlemail.com>wrote:

> 2009/4/15 Srijayanth Sridhar <srijayanth@gmail.com>:
> > 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
>
> This rescue does not make sense. Because the code is invoked once
> upon OptionParser.new. Parsing errors are thrown from parse and
> parse!.
>
> > 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.
>
> 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
>
> --
> remember.guy do |as, often| as.you_can - without end
> http://blog.rubybestprac...
>
>

Brian Candler

4/15/2009 12:58:00 PM

0

Robert Klemme 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/QuickR...

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

Robert Klemme

4/15/2009 1:11:00 PM

0

2009/4/15 Brian Candler <b.candler@pobox.com>:
> Robert Klemme 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

--
remember.guy do |as, often| as.you_can - without end
http://blog.rubybestprac...