What does this warning actually mean?

  • Thread starter Michael T. Richter
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M

Michael T. Richter

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So, I'm trying my hand at metaprogramming and am finding this the result
of executing my code with -w enabled:

warning: class variable access from toplevel singleton method

(This is spammed ad infinitum anywhere I use the overridden gets, but
it's always the same message and always the same cause: gets.)

The code it's pointing to looks like this:

def override_methods(io_in)
puts io_in
class << io_in
alias :eek:ld_gets :gets
@@override_buffer=3D[]
def gets separator =3D $/
raise ArgumentError, "cannot use non-standard
separator" unless separator =3D=3D $/

unless line =3D @@override_buffer.shift
return old_gets
else
return line
end
end
def find_end
for a in 1..20
line =3D self.old_gets
if line =3D=3D "__END__\n"
@@override_buffer =3D []
break
else
@@override_buffer << line
end
end
self
end
end
io_in
end

def find_block_begin io_in
io_in =3D override_methods(io_in)
io_in.find_end
end

To me the culprit is likely that @@override_buffer thing, but I can't
for the life of me figure out how to get around it. My modified gets
needs access to that (shared) buffer that the added find_end method
generates while peeking ahead. @override_buffer and override_buffer
don't work (the latter for reasons obvious to me, the former ... not so
obvious).

Now, the output of the code is exactly what I expect it to be, so this
isn't a show-stopper. I am, however, in the habit of making my code -w
clean if it's at all possible. How would I do it with that snippet?

--=20
Michael T. Richter <[email protected]> (GoogleTalk:
(e-mail address removed))
In his errors a man is true to type. Observe the errors and you will
know the man. (=E5=AD=94=E5=A4=AB=E5=AD=90)

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So, I'm trying my hand at metaprogramming and am finding this the result of=
executing my code with -w enabled:<BR>
<BR>
<TT><B>warning: class variable access from toplevel singleton method</B></T=
T><BR>
<BR>
(This is spammed ad infinitum anywhere I use the overridden gets, but it's =
always the same message and always the same cause: gets.)<BR>
<BR>
The code it's pointing to looks like this:<BR>
<BR>
<TT>def override_methods(io_in)</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; alias :eek:ld_gets :gets</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; @@override_buffer=3D[]</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; def gets separator =3D $/</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; raise A=
rgumentError, &quot;cannot use non-standard separator&quot; unless separato=
r =3D=3D $/</TT><BR>
<BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; unless =
line =3D @@override_buffer.shift</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return old_gets</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; else</T=
T><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; return line</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; end</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; def find_end</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; for a i=
n 1..20</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; line =3D self.old_gets</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; if line =3D=3D &quot;__END__\n&quo=
t;</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp; @@override_buffer =3D []</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp; break</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; else</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp; @@override_buffer &lt;&lt; line</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&n=
bsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; end</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; self</T=
T><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp=
;&nbsp;&nbsp;&nbsp; end</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; end</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; io_in</TT><BR>
<TT>end</TT><BR>
<BR>
<TT>def find_block_begin io_in</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; io_in =3D override_methods(i=
o_in)</TT><BR>
<TT>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; io_in.find_end</TT><BR>
<TT>end</TT><BR>
<BR>
To me the culprit is likely that @@override_buffer thing, but I can't for t=
he life of me figure out how to get around it.&nbsp; My modified gets needs=
access to that (shared) buffer that the added find_end method generates wh=
ile peeking ahead.&nbsp; @override_buffer and override_buffer don't work (t=
he latter for reasons obvious to me, the former ... not so obvious).<BR>
<BR>
Now, the output of the code is exactly what I expect it to be, so this isn'=
t a show-stopper.&nbsp; I am, however, in the habit of making my code -w cl=
ean if it's at all possible.&nbsp; How would I do it with that snippet?<BR>
<BR>
<TABLE CELLSPACING=3D"0" CELLPADDING=3D"0" WIDTH=3D"100%">
<TR>
<TD>
-- <BR>
<B>Michael T. Richter</B> &lt;<A HREF=3D"mailto:[email protected]">ttmri=
(e-mail address removed)</A>&gt; (<B>GoogleTalk:</B> (e-mail address removed))<BR>
<I>In his errors a man is true to type. Observe the errors and you will kno=
w the man. (孔夫子)</I>
</TD>
</TR>
</TABLE>
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M

Michael T. Richter

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Michael I got no clue what you are trying to do here, but maybe the
following is hint enouh, BTW, just do not use class variables ;).
522/23 > cat test1.rb && ruby test1.rb
=20
class << self
@@a=3D42
def a
@@a +=3D1
end
end
puts a
test1.rb:3: warning: class variable access from toplevel singleton method
test1.rb:5: warning: class variable access from toplevel singleton method
test1.rb:5: warning: class variable access from toplevel singleton method
43
=20
---------------------------------------------
=20
523/24 > cat test2.rb && ruby test2.rb
=20
class << self
def a
@a||=3D42
@a+=3D1
end
end
puts a
=20
=20
43


This much I figured out for myself, Robert. ;) The problem is that I
need to share a variable across two functions -- a buffer, to be
precise. One function fills the buffer while the other consumes from
it. The functions are to be singleton methods on an instantiated IO
object. I can't see how to make them share an instance variable without
doing funky things like calling instance_variable_set on the object to
provide it with said instance variable before adding the singletons.
Using a class variable was a desperate test after running headlong into
a brick wall trying to share them.

As it is now, I've got it working with an additional call to
instance_variable_set before defining the singletons, but it looks kind
of clunky and I was hoping there was a more elegant approach available.


--=20
Michael T. Richter <[email protected]> (GoogleTalk:
(e-mail address removed))
Our outrage at China notwithstanding, we should remember that before
1891 the copyrights of foreigners were not protected in the United
States. (Lawrence Lessig)

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On Thu, 2007-02-08 at 22:04 +0900, Robert Dober wrote:
<BLOCKQUOTE TYPE=3DCITE>
<PRE>
<FONT COLOR=3D"#000000">Michael I got no clue what you are trying to do her=
e, but maybe the</FONT>
<FONT COLOR=3D"#000000">following is hint enouh, BTW, just do not use class=
variables ;).</FONT>
<FONT COLOR=3D"#000000">522/23 &gt; cat test1.rb &amp;&amp; ruby test1.rb</=
FONT>

<FONT COLOR=3D"#000000"> class &lt;&lt; self</FONT>
<FONT COLOR=3D"#000000"> @@a=3D42</FONT>
<FONT COLOR=3D"#000000"> def a</FONT>
<FONT COLOR=3D"#000000"> @@a +=3D1</FONT>
<FONT COLOR=3D"#000000"> end</FONT>
<FONT COLOR=3D"#000000"> end</FONT>
<FONT COLOR=3D"#000000"> puts a</FONT>
<FONT COLOR=3D"#000000">test1.rb:3: warning: class variable access from top=
level singleton method</FONT>
<FONT COLOR=3D"#000000">test1.rb:5: warning: class variable access from top=
level singleton method</FONT>
<FONT COLOR=3D"#000000">test1.rb:5: warning: class variable access from top=
level singleton method</FONT>
<FONT COLOR=3D"#000000">43</FONT>


<FONT COLOR=3D"#000000">523/24 &gt; cat test2.rb &amp;&amp; ruby test2.rb</=
FONT>

<FONT COLOR=3D"#000000"> class &lt;&lt; self</FONT>
<FONT COLOR=3D"#000000"> def a</FONT>
<FONT COLOR=3D"#000000"> @a||=3D42</FONT>
<FONT COLOR=3D"#000000"> @a+=3D1</FONT>
<FONT COLOR=3D"#000000"> end</FONT>
<FONT COLOR=3D"#000000"> end</FONT>
<FONT COLOR=3D"#000000"> puts a</FONT>


<FONT COLOR=3D"#000000">43</FONT>
</PRE>
</BLOCKQUOTE>
<BR>
This much I figured out for myself, Robert.&nbsp; <IMG SRC=3D"cid:118606421=
(e-mail address removed)" ALIGN=3D"middle" ALT=3D";)" BORDER=
=3D"0">&nbsp; The problem is that I need to share a variable across <B>two<=
/B> functions -- a buffer, to be precise.&nbsp; One function fills the buff=
er while the other consumes from it.&nbsp; The functions are to be singleto=
n methods on an instantiated IO object.&nbsp; I can't see how to make them =
share an instance variable without doing funky things like calling instance=
_variable_set on the object to provide it with said instance variable befor=
e adding the singletons.&nbsp; Using a class variable was a desperate test =
after running headlong into a brick wall trying to share them.<BR>
<BR>
As it is now, I've got it working with an additional call to instance_varia=
ble_set before defining the singletons, but it looks kind of clunky and I w=
as hoping there was a more elegant approach available.<BR>
<BR>
<BR>
<TABLE CELLSPACING=3D"0" CELLPADDING=3D"0" WIDTH=3D"100%">
<TR>
<TD>
-- <BR>
<B>Michael T. Richter</B> &lt;<A HREF=3D"mailto:[email protected]">ttmri=
(e-mail address removed)</A>&gt; (<B>GoogleTalk:</B> (e-mail address removed))<BR>
<I>Our outrage at China notwithstanding, we should remember that before 189=
1 the copyrights of foreigners were not protected in the United States. (La=
wrence Lessig)</I>
</TD>
</TR>
</TABLE>
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