Ruby Programming Language :: Ruby problem with conditional ranges


	Ruby problem with conditional ranges I'm running into a problem doing a conditional range in ruby. The sample code is: #!/usr/bin/ruby ## one ## two ## three ## four ## five File.open($0, 'r') { \|f\| while f.gets print $_.sub(/^##/, '') if /^## two/ .. /^## four/ end } I'm expecting: two three four but I get the whole file with the leading pound signs stripped off. What's wrong here? -- "Oh, look: rocks!" -- Doctor Who, "Destiny of the Daleks" Hi, At Mon, 4 Jun 2007 15:56:31 +0900, Todd A. Jacobs wrote in [ruby-talk:254228]: > print $_.sub(/^##/, '') if /^## two/ .. /^## four/ print $_.sub(/^##/, '') if ~/^## two/ .. ~/^## four/ > but I get the whole file with the leading pound signs stripped off. > What's wrong here? Because Range object isn't nil nor false, and you'd see a warning if you run with -w option. warning: range literal in condition -- Nobu Nakada Hi, Implicit match against "$_" is not anymore supported in version 1.8. You cas still use it in command line form (with "-e" option). In regular file, you have to write the match explicitly : ## one ## two ## three ## four ## five File.open($0, 'r') { \|f\| while f.gets print $_.sub(/^##/, '') if ($_ =~ /^## two/) .. ($_ =~ /^## four/) end } On 4 juin, 08:56, "Todd A. Jacobs" <tjacobs-sndr-019@codegnome.org> wrote: - Hide quoted text - > I'm running into a problem doing a conditional range in ruby. The sample > code is: > #!/usr/bin/ruby > ## one > ## two > ## three > ## four > ## five > File.open($0, 'r') { \|f\| > while f.gets > print $_.sub(/^##/, '') if /^## two/ .. /^## four/ > end > } > I'm expecting: > two > three > four > but I get the whole file with the leading pound signs stripped off. > What's wrong here? > -- > "Oh, look: rocks!" > -- Doctor Who, "Destiny of the Daleks" On Mon, Jun 04, 2007 at 04:35:25PM +0900, come wrote: > Implicit match against "$_" is not anymore supported in version 1.8. Thanks. Your explanation was very helpful. It works better now, but the range operator still catches more than it should. For example: #!/usr/bin/ruby -w ## one ## two ## three ## four ## five File.open($0) do \|file\| while file.gets print $_.sub(/^## /, '') if ($_ =~ /^## two/)...($_ =~ /^## four/) end end prints up to "four" when (as I understand it) it should stop at "three" since "## four" would make the if-statement false. Am I still missing something obvious? -- "Oh, look: rocks!" -- Doctor Who, "Destiny of the Daleks" On Jun 4, 9:51 pm, "Todd A. Jacobs" <tjacobs- sndr-019@codegnome.org> wrote: > On Mon, Jun 04, 2007 at 04:35:25PM +0900, come wrote: > prints up to "four" when (as I understand it) it should stop at "three" > since "## four" would make the if-statement false. Am I still missing > something obvious? Yes. That will never work, as this is not Perl nor are you creating a range of regexp (which cannot be done, btw). See what happens when the match does happen as you want: irb> a = 'four' irb> (a =~ /two/)...(a =~ /four/) ArgumentError: bad value for range [result is: (nil...'four') ] Plus the uncommented # in the regex are probably making ruby assume a comment. This is another way of writing what you want to do: #!/usr/bin/ruby -w ## one ## two ## three ## four ## five File.open($0) do \|file\| range = [ '$_ =~ /^## two/', '$_ !~ /^## four/' ] while file.gets if eval("#{range[0]}") print $_.sub(/^## /, ''); range.shift end end end Sorry. Buggy code posted. Here's a correct implementation. #!/usr/bin/ruby -w ## one ## two ## three ## five ## six ## four ## five File.open($0) do \|file\| while file.gets if $_ =~ /^## two/ loop { print $_.sub(/^## /, '') file.gets break if not $_ or $_ =~ /^## four/ } end end end Yes, because (as with Perl) there are two forms of conditional range: ".." and "...". The three dots form evaluate the condition after the code. Therefore, the "four" is printed, then the condition is evaluated to false. The two dots form evaluates the condition before the code. So it should works as you expect : "($_ =~ /^## two/)..($_ =~ /^## four/)". On 5 juin, 02:51, "Todd A. Jacobs" - Hide quoted text - > range operator still catches more than it should. For example: > #!/usr/bin/ruby -w > ## one > ## two > ## three > ## four > ## five > File.open($0) do \|file\| > while file.gets > print $_.sub(/^## /, '') if > ($_ =~ /^## two/)...($_ =~ /^## four/) > end > end > prints up to "four" when (as I understand it) it should stop at "three" > since "## four" would make the if-statement false. Am I still missing > something obvious? > -- > "Oh, look: rocks!" > -- Doctor Who, "Destiny of the Daleks"