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Date: Sun, 20 Mar 2011 11:22:21 -0700 (PDT)
From: "Josep M. Bach" <josep.m.b...@gmail.com>
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To: rubinius-dev@googlegroups.com
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Subject: Kernel#gsub not working properly with a block
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Hi there!

The following spec does not pass on rbx (in 
spec/ruby/core/kernel/gsub_spec.rb#78):

  describe "Kernel#gsub with pattern and block" do
    it "acts similarly to using $_.gsub" do
      $_ = "olleh dlrow"
      gsub(/(\w+)/){ $1.reverse }
      $_.should == "hello world"
    end
  end

Trying to fix this one, I found that there is a comparison of replacement 
(in this case it is nil, because gsub is passed a block instead of a 
replacement string) with undefined, which always evaluates to false (even if 
it is nil). Since I don't know really well what `undefined` is, I've first 
tried comparing replacement to nil, which seems to work (in 
kernel/common/string.rb#902):

  def gsub(pattern, replacement=undefined)
    # ...
    if replacement.nil? # was if replacement == undefined 

Now the problem is that, when evaling the block { $1.reverse }, $1 is nil. 
Upon further inspection, This happens just before evaling the block, where 
Regexp's last match is (unsuccessfully) set to the intended match data (same 
file, #939):

      if use_yield
        # Although `match` contains actual match data,
        Regexp.last_match = match
        # Here Regexp.last_match is nil.
        
        # So this block evaluation will fail when trying to do nil.reverse
        val = yield(match.to_s)

I've tried it in the rbx console, so it seems Regexp.last_match=(matchdata) 
(although it returns the passed matchdata) does nothing to Regexp.last_match 
(it keeps previous matched data, or nil if it was nil).

I've checked the regexp.cpp file but I'm no expert there, so I can't tell 
what's wrong....

Any thoughts?

 

 

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<div>Hi there!</div><div><br></div>The following spec does not pass on rbx =
(in <font class=3D"Apple-style-span" face=3D"'courier new', monospace">spec=
/ruby/core/kernel/gsub_spec.rb#78)</font>:<div><blockquote><font class=3D"A=
pple-style-span" face=3D"'courier new', monospace">&nbsp;&nbsp;describe "Ke=
rnel#gsub with pattern and block" do<br>&nbsp;&nbsp; &nbsp;it "acts similar=
ly to using $_.gsub" do<br>&nbsp;&nbsp; &nbsp; &nbsp;$_ =3D "olleh dlrow"<b=
r>&nbsp;&nbsp; &nbsp; &nbsp;gsub(/(\w+)/){ $1.reverse }<br>&nbsp;&nbsp; &nb=
sp; &nbsp;$_.should =3D=3D "hello world"<br>&nbsp;&nbsp; &nbsp;end<br>&nbsp=
;&nbsp;end</font></blockquote></div><div>Trying to fix this one, I found th=
at there is a comparison of replacement (in this case it is nil, because gs=
ub is passed a block instead of a replacement string) with undefined, which=
 always evaluates to false (even if it is nil). Since I don't know really w=
ell what `undefined` is, I've first tried comparing replacement to nil, whi=
ch seems to work (in kernel/common/string.rb#902):</div><div><br></div><div=
><blockquote>&nbsp;<font class=3D"Apple-style-span" face=3D"'courier new', =
monospace">&nbsp;def gsub(pattern, replacement=3Dundefined)<br>&nbsp;&nbsp;=
 &nbsp;# ...<br>&nbsp;&nbsp; &nbsp;if replacement.nil? # was if replacement=
 =3D=3D undefined</font>&nbsp;</blockquote><div>Now the problem is that, wh=
en evaling the block <font class=3D"Apple-style-span" face=3D"'courier new'=
, monospace">{ $1.reverse }, $1</font>&nbsp;is nil. Upon further inspection=
, This happens just before evaling the block, where Regexp's last match is =
(unsuccessfully) set to the intended match data (same file, #939):</div><di=
v><blockquote><font class=3D"Apple-style-span" face=3D"'courier new', monos=
pace">&nbsp;&nbsp; &nbsp; &nbsp;if use_yield<br>&nbsp;&nbsp; &nbsp; &nbsp; =
&nbsp;# Although `match` contains actual match data,<br>&nbsp;&nbsp; &nbsp;=
 &nbsp; &nbsp;Regexp.last_match =3D match<br>&nbsp;&nbsp; &nbsp; &nbsp; &nb=
sp;# Here Regexp.last_match is nil.<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;<br=
>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;# So this block evaluation will fail when=
 trying to do nil.reverse<br>&nbsp;&nbsp; &nbsp; &nbsp; &nbsp;val =3D yield=
(match.to_s)</font></blockquote></div><div>I've tried it in the rbx console=
, so it seems Regexp.last_match=3D(matchdata) (although it returns the pass=
ed matchdata) does nothing to Regexp.last_match (it keeps previous matched =
data, or nil if it was nil).</div><div><br></div><div>I've checked the rege=
xp.cpp file but I'm no expert there, so I can't tell what's wrong....</div>=
<div><br></div><div>Any thoughts?</div><blockquote>&nbsp;</blockquote><div>=
&nbsp;</div></div>
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