gmane.comp.lang.ruby.general

coderrr | 16 May 00:02

Matz: can we have rescue/else/ensure available in all blocks?

Hi Matz,

I recently posted a Ruby 1.9 wishlist (http://groups.google.com/group/
ruby-talk-google/browse_thread/thread/d771ffa9fe10b811/
c8b5b0b02bd1e2d4) and the #1 item was to have rescue/else/ensure
available in all blocks w/o the need for begin/end.  It turned out to
be the one thing that everyone agreed on.  I think anyone who has done
a real project in Ruby has run into this.

Is there any way you can get this in 1.9?

This (contrived example):

pages.each do |page|
  page.links.each do |link|
    process link
  rescue MalformedLinkError
    @bad_links << link
  end
rescue MalformedPageError
  @bad_pages << page
end

Is so much nicer than this:

pages.each do |page|
  begin
    page.links.each do |link|
      begin
        process link

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Yukihiro Matsumoto | 16 May 01:16

Re: Matz: can we have rescue/else/ensure available in all blocks?

Hi,

In message "Re: Matz: can we have rescue/else/ensure available in all blocks?"
    on Fri, 16 May 2008 07:02:47 +0900, coderrr <coderrr.contact <at> gmail.com> writes:

|This (contrived example):
|
|pages.each do |page|
|  page.links.each do |link|
|    process link
|  rescue MalformedLinkError
|    @bad_links << link
|  end
|rescue MalformedPageError
|  @bad_pages << page
|end

can be considered as 

  pages.each do |page|
    begin
      page.links.each do |link|
        begin
          process link
        rescue MalformedLinkError
          @bad_links << link
        end
      end
    rescue MalformedPageError
      @bad_pages << page

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coderrr | 16 May 02:02

Re: Matz: can we have rescue/else/ensure available in all blocks?

Hey Matz,

Thanks a lot for the quick reply.

I agree it is possible that someone who doesn't know the syntax could
potentially misinterpret these things.  I think though, that this should be
weighed against the benefit of adding it to the language.  I assume it's
your judgment that the cost outweighs the benefit on this?  I of course
think the opposite :)

I wonder what other developers think about how easily confused these would
be, and about how that weighs against the benefits?

The benefits are more concise syntax (which is the thing I love most about
ruby), removing 2 lines and an indentation for a lot of rescue statements

Also, I would be happy if only the ability to rescue were added to all
blocks but begin/end were required for else/ensure since they are less
commonly used.

- steve
http://coderrr.wordpress.com

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Peter Jones | 16 May 03:30

Re: Matz: can we have rescue/else/ensure available in all blocks?

coderrr <coderrr.contact <at> gmail.com> writes:
> pages.each do |page|
>   begin
>     page.links.each do |link|
>       begin
>         process link
>       rescue MalformedLinkError
>         @bad_links << link
>       end
>     end
>   rescue MalformedPageError
>     @bad_pages << page
>   end
> end

If you write code that looks like that, maybe you should give Java a
second look ;)

Seriously though, you could easily restructure your code to be a bit
more OO and then you wouldn't have to worry about rescuing exceptions
all over the place, including several times in nested loops.

--

-- 
Peter Jones [pjones at domain below]
pmade inc. - http://pmade.com

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coderrr | 16 May 04:52

Re: Matz: can we have rescue/else/ensure available in all blocks?

>
> If you write code that looks like that, maybe you should give Java a
> second look ;)
>
> Seriously though, you could easily restructure your code to be a bit
> more OO and then you wouldn't have to worry about rescuing exceptions
> all over the place, including several times in nested loops.
>

It was a contrived example.  So would that be a "not in favor of" from you
Peter?

- steve
http://coderrr.wordpress.com

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Michael Neumann | 16 May 12:10

Re: Matz: can we have rescue/else/ensure available in all blocks?

coderrr wrote:
 >> If you write code that looks like that, maybe you should give Java a
 >> second look ;)
 >>
 >> Seriously though, you could easily restructure your code to be a bit
 >> more OO and then you wouldn't have to worry about rescuing exceptions
 >> all over the place, including several times in nested loops.
 >>
 >
 > It was a contrived example.  So would that be a "not in favor of" 
from you
 > Peter?

How would you have "rescue" and "ensure" blocks when using "{" and "}",
both of which are (almost) equivalent to "do" and "end"?

   pages.each {|page|
      ...
   }

Regards,

   Michael

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coderrr | 17 May 01:31

Re: Matz: can we have rescue/else/ensure available in all blocks?

> How would you have "rescue" and "ensure" blocks when using "{" and "}",
> both of which are (almost) equivalent to "do" and "end"?
>
>  pages.each {|page|
>     ...
>  }
>
>
pages.each { |page|
rescue SomeError
...
ensure
...
}

Or you could just not allow it for { }, only for do/end.  I agree it looks
weird, and is probably more confusing when using it with { }.

- steve
http://coderrr.wordpress.com

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Peter Jones | 16 May 16:45

Re: Matz: can we have rescue/else/ensure available in all blocks?

coderrr <coderrr.contact <at> gmail.com> writes:
> It was a contrived example.  So would that be a "not in favor of" from you
> Peter?

I'm certainly not convinced.  Maybe you could post a more real world
example because I'm having a hard time seeing the usefulness in nested
rescues.

--

-- 
Peter Jones [pjones at domain below]
pmade inc. - http://pmade.com

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coderrr | 17 May 02:04

Re: Matz: can we have rescue/else/ensure available in all blocks?

> I'm certainly not convinced.  Maybe you could post a more real world
> example because I'm having a hard time seeing the usefulness in nested
> rescues.
>
>
This has nothing to do with nested rescues.  I merely used that in the
example to make it more compelling, although I guess for you it did the
opposite :P

Here's how you can get some real world examples:
cat > findem.rb <<EOF
ARGV.each do |fn|
  data = File.read(fn)
  ms = data.scan(%r{
            do \s* (?:\| [^|]* \|)+ \s*
                begin
                  (?:(?!end).)+?
                end \s*
            end
             }mx)

  if ! ms.empty?
    puts fn
    ms.each{|m| puts m }
  end
end
EOF

find /usr/lib/ruby/gems/1.8/gems -name "*.rb" | xargs ruby findem.rb >
the_real_world

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coderrr | 17 May 02:09

Re: Matz: can we have rescue/else/ensure available in all blocks?

>             do \s* (?:\| [^|]* \|)+ \s*

sorry, this line should read:

 do \s* (?:\| [^|]* \|)? \s*

after that, I get 67 results instead of 43

- steve
http://coderrr.wordpress.com

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Peter Jones | 17 May 03:40

Re: Matz: can we have rescue/else/ensure available in all blocks?

coderrr <coderrr.contact <at> gmail.com> writes:
> find /usr/lib/ruby/gems/1.8/gems -name "*.rb" | xargs ruby findem.rb >
> the_real_world

Ah, now I know why.  I ran this on ~/ and it only showed lines in a
few gems that I happened to have lying around, but nothing in my code.

I guess it's just not an idiom that I use.  That might be because my
background, I tend to use exceptions most often for situations that
can't be recovered from.

I'm not suggesting that you do, but I know a lot of people use
exceptions as high-level flow control, which I find disturbing.

Thanks for the code searcher.

--

-- 
Peter Jones [pjones at domain below]
pmade inc. - http://pmade.com

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coderrr | 17 May 07:46

Re: Matz: can we have rescue/else/ensure available in all blocks?

btw, that script _will_ give some false positives when there are other
blocks/ifs/whiles inside the block in question but for me those made
up less than 5% of the results

- steve
http://coderrr.wordpress.com