Reading String Data as a File
in [Ruby]
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From: Robert Klemme on 30 Jun 2010 12:30 On 30.06.2010 17:31, Brian Candler wrote: > Robert Klemme wrote: >> 2010/6/30 Brian Candler<b.candler(a)pobox.com>: >>> or rather: >>> >>> Tempfile.open "prefix", "/tmp" do |io| >>> �io.write everything >>> �io.flush >> >> I'd rather io.close instead of io.flush to release resources as soon >> as possible. > > But tempfile will want to close itself using the block form anyway. Yes, but later. This can make a difference if you are low on file descriptors. And you do not risk weird effects by the same process opening the file twice. > In most versions of ruby, Tempfile with a block returns nil. A change > was committed so that it returns the (closed) object, but that hasn't > made it into either of the versions I have lying around here. > >>> tf = Tempfile.open("aaa","/tmp") { puts "hello"; 123 } > hello > => nil The non block form obviously returns the Tempfile instance and if you want it to be returned from the block what stops you from explicitly returning it? IMHO the method with block should return whatever the implementor of the block chooses. That is far more reusable than always returning the Tempfile. Most of the time the Tempfile instance is of no use anyway since it is closed then. Kind regards robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/
From: Robert Klemme on 30 Jun 2010 12:32 On 30.06.2010 17:05, James Edward Gray II wrote: > > That's mostly due to a pet peeve of mine. I often see code that > slurps when foreach() would have worked fine. That's why I try to > push that as a first choice. I wholeheartedly agree. > Do you think it would help if I added Wrapping an IO under the > Shortcut Interface on this page? > > http://fastercsv.rubyforge.org/classes/FasterCSV.html +1 robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/
From: Brian Candler on 30 Jun 2010 14:26 Robert Klemme wrote: > The non block form obviously returns the Tempfile instance and if you > want it to be returned from the block what stops you from explicitly > returning it? Only that it's a bit verbose: tf = nil Tempfile.open(...) do |io| tf = io ... end puts tf.path http://redmine.ruby-lang.org/issues/show/504 > IMHO the method with block should return whatever the implementor of the > block chooses. That is far more reusable than always returning the > Tempfile. Maybe that's what the accepted patch does - I haven't tested it. It would be consistent with File.open { ... } if it worked that way. Anyway, I think we're talking about minutiae. You say that one should close the file at the earliest opportunity to "save resources", but the only resource we're talking about is one slot in the kernel file descriptor table, and most apps aren't going to be constrained by that. -- Posted via http://www.ruby-forum.com/.
From: Robert Klemme on 30 Jun 2010 15:32 On 30.06.2010 20:26, Brian Candler wrote: > Robert Klemme wrote: >> The non block form obviously returns the Tempfile instance and if you >> want it to be returned from the block what stops you from explicitly >> returning it? > > Only that it's a bit verbose: > > tf = nil > Tempfile.open(...) do |io| > tf = io > ... > end > puts tf.path No, I was talking about the other version which returns whatever the block returns. You would do tf = Tempfile.open(...) do |io| ... io end puts tf.path > http://redmine.ruby-lang.org/issues/show/504 Apparently people differ in their preferences. >> IMHO the method with block should return whatever the implementor of the >> block chooses. That is far more reusable than always returning the >> Tempfile. > > Maybe that's what the accepted patch does - I haven't tested it. It > would be consistent with File.open { ... } if it worked that way. Exactly that is what the patch does: http://redmine.ruby-lang.org/repositories/diff/ruby-19?rev=19454 > Anyway, I think we're talking about minutiae. You say that one should > close the file at the earliest opportunity to "save resources", but the > only resource we're talking about is one slot in the kernel file > descriptor table, and most apps aren't going to be constrained by that. That's true. But I also have seen issues caused by files being opened more than once by the same process. Plus, you'll notice much faster if you try to write to the tempfile after you thought you were done when you close the file. If the code is more complicated these bugs can be hard to track. How much simpler is it if you see this: irb(main):006:0> Tempfile.open "x" do |io| irb(main):007:1* p io irb(main):008:1> io.puts "hello" irb(main):009:1> io.close irb(main):010:1> io.puts "world" irb(main):011:1> end #<File:C:/Users/Robert/x20100630-4456-1ixsj0i-0> IOError: closed stream from (irb):10:in `block in irb_binding' from /usr/local/lib/ruby19/1.9.1/tempfile.rb:199:in `open' from (irb):6 from /usr/local/bin/irb19:12:in `<main>' It's probably not that big a deal but I believe such discussions bring benefit to the community by presenting alternative solutions to a problem along with arguments. I always like this food for thought. Thanks for sharing your thoughts! Kind regards robert -- remember.guy do |as, often| as.you_can - without end http://blog.rubybestpractices.com/
From: James Edward Gray II on 30 Jun 2010 20:45
On Jun 30, 2010, at 10:41 AM, Brian Candler wrote: > James Edward Gray II wrote: >> I'm open to suggestions and I do take patches. > > Specifically, I'd like to see how to parse CSV from stdin. You provide > an example in the opposite direction: > > # FCSV($stderr) { |csv_err| csv_err << %w{my data here} } # to > $stderr On Jun 30, 2010, at 11:35 AM, Robert Klemme wrote: > On 30.06.2010 17:05, James Edward Gray II wrote: >> >> Do you think it would help if I added Wrapping an IO under the >> Shortcut Interface on this page? >> >> http://fastercsv.rubyforge.org/classes/FasterCSV.html > > +1 Better? http://fastercsv.rubyforge.org/classes/FasterCSV.html James Edward Gray II |