A Syntax question

ruby-talk
1

Hey Guys,

I would have thought the following two code snippets were equivalent.
However, only the first one will raise err. Can someone explain to me
how I should be 'reading' the 2nd snippet?

      rescue Exception => err
        begin
            RDoc::usage
        rescue SystemExit
        end
        raise err

      rescue Exception => err
        begin RDoc::usage rescue SystemExit end
        raise err

Sonny.

···

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2

This may be wrong, but this works:

begin
  raise err
rescue Exception => err
  begin
    puts "bummer 1"
    raise err2
  rescue Exception => err2
    puts "bummer 1.1"
  end
end

.vs.

begin
  raise err
rescue Exception => err
  begin puts "bummer 2"; raise err2; rescue Exception =>err2; puts
"bummer 2.1"; end
end

···

On Apr 4, 1:01 pm, Sonny Chee <sonny.c...@gmail.com> wrote:

Hey Guys,

I would have thought the following two code snippets were equivalent.
However, only the first one will raise err. Can someone explain to me
how I should be 'reading' the 2nd snippet?

      rescue Exception => err
        begin
            RDoc::usage
        rescue SystemExit
        end
        raise err

      rescue Exception => err
        begin RDoc::usage rescue SystemExit end
        raise err

Sonny.

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3

These are two different syntactic constructions.

       <expression1> rescue <expression2>

returns the value of <expression1>, unless there is an exception in which
case it returns the value of <expression2>

In this construct, you cannot specify the exception class. I think it only
catches StandardError and subclasses.

Typical usage:

     foo rescue nil # just ignore StandardError

     a = foo rescue bar rescue baz # return value from foo, if exception
                                    # then bar, if exception then baz

Regards,

Brian.

···

On Thu, Apr 05, 2007 at 03:01:56AM +0900, Sonny Chee wrote:

Hey Guys,

I would have thought the following two code snippets were equivalent.
However, only the first one will raise err. Can someone explain to me
how I should be 'reading' the 2nd snippet?

      rescue Exception => err
        begin
            RDoc::usage
        rescue SystemExit
        end
        raise err

      rescue Exception => err
        begin RDoc::usage rescue SystemExit end
        raise err

4

Thanks Dale. I'm not actually looking for a workaround. Snippet #1 of
my original post does work. I'm trying to understand why snippet #2
doesn't.

The only difference between the two are the whitespaces. If someone
could help me understand how snippet #2 is being parsed/read by the
interpretter that would be super.

···

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5

Awesome. That clarifies things. Thanks Brian.

···

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