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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Mithum,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>You say:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal style='margin-left:.5in;text-indent:-.25in;mso-list:l0 level1 lfo1'><![if !supportLists]><font
size=2 color=navy face=Wingdings><span style='font-size:10.0pt;font-family:
Wingdings;color:navy'><span style='mso-list:Ignore'>Ø<font size=1
face="Times New Roman"><span style='font:7.0pt "Times New Roman"'>
</span></font></span></span></font><![endif]><font size=2 color=navy
face=Arial><span style='font-size:10.0pt;font-family:Arial;color:navy'>. . . </span></font><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'>demonstrating
that it is </span></font><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>use warnings</span></font><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> which would
help more in this scenario rather than use strict.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>No, you haven’t demonstrated that at
all.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>On the one hand, you are assuming that “require”
is just like ‘C’ language “#include” (a pre-processor
directive,) but on the other hand you have ended the module with “1;”
which indicates you know that “require” is not just like “#include”.
The instruction “require” is not a pre-processing directive, but
rather, the required file is compiled and executed at the time of inclusion,
and the whole process retains the integrity of the file as a unit of
scope. So . . .<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>From my e-mail:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>> Get in the habit of putting the
following at the top of every file:</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>>
use strict;</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>If you actually do that, i.e. if you put
it at the head of the file “newbie.pm”, you will get this message:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:navy'>Global symbol
"$c" requires explicit package name at newbie.pm line 5.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New";color:navy'>Compilation
failed in require at a.pl line 7.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>That is a compile time message dealing
with declaration. By contrast, “use warnings” is a run time
check and has nothing to do with the declaration, except that it calls
attention to your mistaken belief that you initialized something that you haven’t.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>By the way, I also put “use warnings”
at the top of all my files during development, and usually I leave it
there. For performance reasons some people take it out aftter development
is done if they have a performance critical app – like I said, it is a
run-time check.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Alexander Danel<o:p></o:p></span></font></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
chicago-talk-bounces+danel=speakeasy.net@pm.org
[mailto:chicago-talk-bounces+danel=speakeasy.net@pm.org] <b><span
style='font-weight:bold'>On Behalf Of </span></b>Mithun Bhattacharya<br>
<b><span style='font-weight:bold'>Sent:</span></b> Friday, March 05, 2010 10:33
PM<br>
<b><span style='font-weight:bold'>To:</span></b> Chicago.pm chatter<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Chicago-talk] Global
variable behavior</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<div>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=2 face=Arial><span
style='font-size:10.0pt;font-family:Arial'>Thanks for the input. I guess I took
somethings for granted and didn't read up the relevant sections carefully :)<br>
<br>
I am not nitpicking here but I would like to share a few more things which
became more obvious to me - hopefully it will help others too.<br>
<br>
New code follows<br>
======================================================================<br>
</span></font><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>$ cat a.pl <br>
use strict;<br>
<br>
push @INC, '.';<br>
<br>
our $c = 15;<br>
<br>
require newbie;<br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'>======================================================================</span></font><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'><br>
<br>
$ cat newbie.pm <br>
package newbie;<br>
<br>
print "first attempt: " . $c . "\n";<br>
print "second attempt: " . $::c . "\n";<br>
<br>
1;<br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'>======================================================================</span></font><font
size=2 face="Courier New"><span style='font-size:10.0pt;font-family:"Courier New"'><br>
<br>
$ perl a.pl <br>
first attempt: <br>
second attempt: 15<br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'>======================================================================<br>
</span></font><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'><br>
$ perl -w a.pl <br>
Use of uninitialized value $newbie::c in concatenation (.) or string at
newbie.pm line 3.<br>
first attempt: <br>
second attempt: 15<br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'>======================================================================<br>
<br>
</span></font><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'>$ perl -v<br>
This is perl, v5.10.0 built for x86_64-linux-thread-multi<br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'>======================================================================<br>
<br>
I am just demonstrating that it is </span></font><font size=2 face="Courier New"><span
style='font-size:10.0pt;font-family:"Courier New"'>use warnings</span></font><font
size=2 face=Arial><span style='font-size:10.0pt;font-family:Arial'> which would
help more in this scenario rather than use strict.<br>
<br>
Something else which confused me after I started understanding our better was
the following - maybe someone can point out if I have miss-understood anything.<br>
<br>
As per perldoc for our<br>
<br>
"our" associates a simple name with a package variable in the<br>
current
package for use within the current scope. When "use<br>
strict
'vars'" is in effect, "our" lets you use declared global<br>
variables
without qualifying them with package names, within the<br>
lexical
scope of the "our" declaration. In this way "our"<br>
differs from
"use vars", which is package scoped.<br>
<br>
Unlike
"my", which both allocates storage for a variable and<br>
associates a
simple name with that storage for use within the<br>
current
scope, "our" associates a simple name with a package<br>
variable in
the current package, for use within the current<br>
scope. In
other words, "our" has the same scoping rules as "my",<br>
but does not
necessarily create a variable.<br>
<br>
The first paragraph seems to imply to me that our is for declaring a global
variable as most C developers tend to think of them. If I understand it
correctly our is always associated with a package - if we call our outside a
defined package as is the case in my sample it goes to the package main.<br>
<br>
The second paragraph doesnt help me understand things any better other than to
say that my and our are similar in scope. I would like to quote from <a
href="http://stackoverflow.com/questions/845060/what-is-the-difference-between-my-and-our-in-perl"
target="_blank">http://stackoverflow.com/questions/845060/what-is-the-difference-between-my-and-our-in-perl</a>
which says<o:p></o:p></span></font></p>
<div style='margin-left:30.0pt'>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Available since Perl 5, my is a way to declare:<o:p></o:p></span></font></p>
<div style='margin-left:30.0pt'>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> * non-package variables, that are<br>
* private,<br>
* new,<br>
* non-global variables,<br>
* separate from any package. So that the variable cannot be
accessed in the form of $package_name::variable.<o:p></o:p></span></font></p>
</div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><br>
On the other hand, our variables are:<o:p></o:p></span></font></p>
<div style='margin-left:30.0pt'>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'> * package variables, and thus
automatically<br>
* global variables,<br>
* definitely not private,<br>
* nor are they necessarily new; and they<br>
* can be accessed outside the package (or lexical scope)
with the qualified namespace, as $package_name::variable.<o:p></o:p></span></font></p>
</div>
</div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'><o:p> </o:p></span></font></p>
</div>
<div>
<p class=MsoNormal><font size=2 face=Arial><span style='font-size:10.0pt;
font-family:Arial'>Personally the second explanation is much more easier for me
to comprehend than the perldoc but I suppose someone could elaborate what I
might be missing out on if I follow that explanation.<br>
<br>
In any case thanks for listening to me and hopefully I am not making a fool of
myself here with perl basics.<br>
</span></font><font size=2 face="Courier New"><span style='font-size:10.0pt;
font-family:"Courier New"'><br>
</span></font><font size=2 face=Arial><span style='font-size:10.0pt;font-family:
Arial'><br>
<br>
- Mithun</span></font><font size=2 face="Courier New"><span style='font-size:
10.0pt;font-family:"Courier New"'><o:p></o:p></span></font></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
<hr size=1 width="100%" align=center>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'> Alexander Danel
<danel@speakeasy.net><br>
<b><span style='font-weight:bold'>To:</span></b> Chicago.pm chatter
<chicago-talk@pm.org><br>
<b><span style='font-weight:bold'>Sent:</span></b> Wed, March 3, 2010 9:00:08
PM<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [Chicago-talk] Global
variable behavior<br>
</span></font><br>
<br>
<o:p></o:p></p>
<meta http-equiv=x-dns-prefetch-control content=off>
<div>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Get in the habit of putting the following
at the top of every file:</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>
use strict;</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Try it. It will inform you that you
are implicitly doing just what you claim you are not doing: you have declared
(or, as you put it “redeclared”) the variable. “Use
strict” will protest because implicit declarations are often an accident;
which is clearly appropriate for your case.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>By the way, I take exception to your
statement “. . . should make it global across all name
spaces.” No such concept exists in Perl. You declared the
variable to be in the “main” namespace; which you seemingly
understood when you used “$::c”, the naked double-colon being an
alias for “main::”. The package “main” is
in force until you declare otherwise.</span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> </span></font><o:p></o:p></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Alexander Danel</span></font><o:p></o:p></p>
<div>
<div class=MsoNormal align=center style='text-align:center'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
</span></font></div>
<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
chicago-talk-bounces+danel=speakeasy.net@pm.org [mailto:chicago-talk-bounces+danel=speakeasy.net@pm.org]
<b><span style='font-weight:bold'>On Behalf Of </span></b>Mithun Bhattacharya<br>
<b><span style='font-weight:bold'>Sent:</span></b> Wednesday, March 03, 2010
8:20 PM<br>
<b><span style='font-weight:bold'>To:</span></b> chicago-talk@pm.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> [Chicago-talk] Global
variable behavior</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
<div>
<div>
<p class=MsoNormal><font size=3 face=Arial><span style='font-size:12.0pt;
font-family:Arial'>Hi Everyone,<br>
<br>
A piece of my code is behaving in a way I didn't expect and I was hoping
someone could enlighten me as to why..<br>
</span></font><br>
-------------------------------------<br>
<font size=2><span style='font-size:10.0pt'>$ cat <a href="http://a.pl"
target="_blank">a.pl</a> <br>
push @INC, '.';<br>
<br>
our $c = 15;<br>
<br>
require newbie;<br>
</span></font>-------------------------------------<br>
<font size=2><span style='font-size:10.0pt'>$ cat <a href="http://newbie.pm"
target="_blank">newbie.pm</a> <br>
package newbie;<br>
<br>
print "first attempt: " . $c . "\n";<br>
print "second attempt: " . $::c . "\n";<br>
<br>
1;<br>
</span></font>-------------------------------------<br>
<font size=2><span style='font-size:10.0pt'>$ perl a.pl <br>
first attempt: <br>
second attempt: 15</span></font><br>
-------------------------------------<br>
<font face=Arial><span style='font-family:Arial'><br>
The way I see it the </span></font><font face="Courier New"><span
style='font-family:"Courier New"'>our</span></font><font face=Arial><span
style='font-family:Arial'> in </span></font><font face="Courier New"><span
style='font-family:"Courier New"'>a.pl</span></font><font face=Arial><span
style='font-family:Arial'> should make it global across all namespaces. The
second attempt does seem to say that did take place. What I am not sure is why
the </span></font><font face="Courier New"><span style='font-family:"Courier New"'>$c</span></font><font
face=Arial><span style='font-family:Arial'> variable has become local in scope
even though I haven't re-declared or redefined it in any way inside </span></font><font
face="Courier New"><span style='font-family:"Courier New"'>newbie.pm</span></font><font
face=Arial><span style='font-family:Arial'>.<br>
<br>
<br>
<br>
<br>
- Mithun</span></font><o:p></o:p></p>
</div>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'> <o:p></o:p></span></font></p>
</div>
</div>
</div>
</div>
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