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

[coderrr]

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
rescue MalformedLinkError
@bad_links << link
end
end
rescue MalformedPageError
@bad_pages << page
end
end

It would make all our lives better! :]

- steve
http://coderrr.wordpress.com

 

[coderrr]

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

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

 

[coderrr]

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

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

 

[Michael Neumann]

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

 

[coderrr]

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

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

 

[coderrr]

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

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

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

for me:
grep \\.rb the_real_world | wc -l
=> 43

- steve
http://coderrr.wordpress.com

 

[coderrr]

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

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

 

[coderrr]

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