OptionParser and Exceptions


#1

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


#2

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


#3

Thanks both of you.

Jayanth

On Wed, Apr 15, 2009 at 5:35 PM, Robert K.


#4

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.


#5

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


#6

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