[29493] in Perl-Users-Digest
Perl-Users Digest, Issue: 737 Volume: 11
daemon@ATHENA.MIT.EDU (Perl-Users Digest)
Thu Aug 9 16:19:37 2007
Date: Thu, 9 Aug 2007 13:19:13 -0700 (PDT)
From: Perl-Users Digest <Perl-Users-Request@ruby.OCE.ORST.EDU>
To: Perl-Users@ruby.OCE.ORST.EDU (Perl-Users Digest)
Perl-Users Digest Thu, 9 Aug 2007 Volume: 11 Number: 737
Today's topics:
Re: pass by reference <mritty@gmail.com>
Re: pass by reference <jgibson@mail.arc.nasa.gov>
Re: pass by reference <uri@stemsystems.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: pass by reference <bpatton@ti.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: pass by reference <uri@stemsystems.com>
Re: pass by reference <uri@stemsystems.com>
Re: pass by reference <uri@stemsystems.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: pass by reference <larry.grant.dc@gmail.com>
Re: Replacing a line <glex_no-spam@qwest-spam-no.invalid>
Re: Size of all files in a directory? <dummy@example.com>
Digest Administrivia (Last modified: 6 Apr 01) (Perl-Users-Digest Admin)
----------------------------------------------------------------------
Date: Thu, 09 Aug 2007 11:16:14 -0700
From: Paul Lalli <mritty@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186683374.978210.80010@q75g2000hsh.googlegroups.com>
On Aug 9, 2:05 pm, Larry <larry.grant...@gmail.com> wrote:
> > Larry <larry.grant...@gmail.com> writes:
> > > The following code snippet shows how I do "pass by
> > > reference" in Perl. It works fine, but I'm wondering...
> > > is there a less verbose way to do this?
> I don't like the $_[0] method, because it doesn't give me a
> chance to name my variables.... I prefer names, not numbers,
> thank you!
So use your name the entire time you're actually doing something with
the variable, then change it back at the end:
$ perl -le'
my $x = 7;
squareMe($x);
print $x;
sub squareMe {
my ($arg) = @_;
$arg **= 2;
$_[0] = $arg;
}
'
49
Paul Lalli
------------------------------
Date: Thu, 09 Aug 2007 11:28:07 -0700
From: Jim Gibson <jgibson@mail.arc.nasa.gov>
Subject: Re: pass by reference
Message-Id: <090820071128077402%jgibson@mail.arc.nasa.gov>
In article <1186682747.757896.223810@o61g2000hsh.googlegroups.com>,
Larry <larry.grant.dc@gmail.com> wrote:
> On Aug 9, 2:04 pm, Peter Makholm <pe...@makholm.net> wrote:
> > Larry <larry.grant...@gmail.com> writes:
> > > The following code snippet shows how I do "pass by reference" in
> > > Perl. It works fine, but I'm wondering... is there a less verbose way
> > > to do this?
> >
> > Perl already implements a kind of pass by reference in the @_
> > argument.
> >
> > #!/usr/bin/perl -l
> > sub squareMe {
> > $_[0] *= $_[0];
>
> I don't like the $_[0] method, because it doesn't give me a chance to
> name my variables.... I prefer names, not numbers, thank you! :)
>
$_ is a name, just not a pronounceable one!
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------------------------------
Date: Thu, 09 Aug 2007 18:59:41 GMT
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: pass by reference
Message-Id: <x7hcn8leji.fsf@mail.sysarch.com>
>>>>> "L" == Larry <larry.grant.dc@gmail.com> writes:
L> I don't like the $_[0] method, because it doesn't give me a chance to
L> name my variables.... I prefer names, not numbers, thank you! :)
so pass in a reference. the typeglob hack you created is fugly and
wasteful. and don't use prototypes as they are not what you want here. a
plain simple reference works fine.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org
------------------------------
Date: Thu, 09 Aug 2007 19:07:12 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186686432.552257.78870@e16g2000pri.googlegroups.com>
On Aug 9, 2:59 pm, Uri Guttman <u...@stemsystems.com> wrote:
> >>>>> "L" == Larry <larry.grant...@gmail.com> writes:
>
> L> I don't like the $_[0] method, because it doesn't give me a chance to
> L> name my variables.... I prefer names, not numbers, thank you! :)
>
> so pass in a reference. the typeglob hack you created is fugly and
> wasteful. and don't use prototypes as they are not what you want here. a
> plain simple reference works fine.
>
I don't want to pass in a reference! You call that "passing by
reference"?! :)
I want to write:
squareMe $foo
not
squareMe \$foo
!!!
------------------------------
Date: Thu, 09 Aug 2007 19:08:19 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186686499.683528.189600@g12g2000prg.googlegroups.com>
On Aug 9, 3:07 pm, Larry <larry.grant...@gmail.com> wrote:
> On Aug 9, 2:59 pm, Uri Guttman <u...@stemsystems.com> wrote:
>
> > >>>>> "L" == Larry <larry.grant...@gmail.com> writes:
>
> > L> I don't like the $_[0] method, because it doesn't give me a chance to
> > L> name my variables.... I prefer names, not numbers, thank you! :)
>
> > so pass in a reference. the typeglob hack you created is fugly and
> > wasteful. and don't use prototypes as they are not what you want here. a
> > plain simple reference works fine.
>
> I don't want to pass in a reference! You call that "passing by
> reference"?! :)
>
> I want to write:
>
> squareMe $foo
>
> not
>
> squareMe \$foo
>
> !!!
And I *do* need the prototypes... that's the only way to get the
reference without my callers having to use backslashes!
------------------------------
Date: Thu, 09 Aug 2007 19:10:37 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186686637.717608.54860@e9g2000prf.googlegroups.com>
On Aug 9, 1:50 pm, Larry <larry.grant...@gmail.com> wrote:
> The following code snippet shows how I do "pass by reference" in
> Perl. It works fine, but I'm wondering... is there a less verbose way
> to do this?
>
> (I know in this simple example, I could avoid the typeglob assignment
> and just use $$arg instead of $arg, but in a more complex usage, that
> would bug me... I'd rather just use the more normal-looking $arg
> everywhere.)
>
> -------------
>
> sub squareMe (\$) {
> my ($argRef) = @_;
> local *arg = $argRef;
> our $arg;
>
> $arg *= $arg;
>
> }
>
> my $n = 7;
> squareMe $n;
> print "$n\n"; # prints 49
I just figured out a somewhat more elegant way:
sub squareMe (\$) {
local (*arg) = @_;
our $arg;
$arg *= $arg;
}
Too bad about the need for having to repeat "arg" in "our" though...
------------------------------
Date: Thu, 09 Aug 2007 12:59:16 -0500
From: Billy Patton <bpatton@ti.com>
Subject: Re: pass by reference
Message-Id: <f9fklk$ksa$1@home.itg.ti.com>
Larry wrote:
> The following code snippet shows how I do "pass by reference" in
> Perl. It works fine, but I'm wondering... is there a less verbose way
> to do this?
>
> (I know in this simple example, I could avoid the typeglob assignment
> and just use $$arg instead of $arg, but in a more complex usage, that
> would bug me... I'd rather just use the more normal-looking $arg
> everywhere.)
>
> -------------
>
> sub squareMe (\$) {
> my ($argRef) = @_;
> local *arg = $argRef;
> our $arg;
>
> $arg *= $arg;
> }
>
> my $n = 7;
> squareMe $n;
> print "$n\n"; # prints 49
>
Do you really want side effects ?
Passing by reference does this.
Guess this is too simple to make that decision.
sub squareMe($) {
my ($arg) = @_;
$arg *= $arg;
}
my $n=7;
$n = squareMe $n; # no side effects
I hate it when my variables get changed somewhere else and I have to
track it down for debugging!
------------------------------
Date: Thu, 09 Aug 2007 19:17:40 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186687060.811271.110820@m37g2000prh.googlegroups.com>
On Aug 9, 1:59 pm, Billy Patton <bpat...@ti.com> wrote:
> Larry wrote:
> > The following code snippet shows how I do "pass by reference" in
> > Perl. It works fine, but I'm wondering... is there a less verbose way
> > to do this?
>
> > (I know in this simple example, I could avoid the typeglob assignment
> > and just use $$arg instead of $arg, but in a more complex usage, that
> > would bug me... I'd rather just use the more normal-looking $arg
> > everywhere.)
>
> > -------------
>
> > sub squareMe (\$) {
> > my ($argRef) = @_;
> > local *arg = $argRef;
> > our $arg;
>
> > $arg *= $arg;
> > }
>
> > my $n = 7;
> > squareMe $n;
> > print "$n\n"; # prints 49
>
> Do you really want side effects ?
> Passing by reference does this.
> Guess this is too simple to make that decision.
>
> sub squareMe($) {
> my ($arg) = @_;
> $arg *= $arg;
>
> }
>
> my $n=7;
> $n = squareMe $n; # no side effects
> I hate it when my variables get changed somewhere else and I have to
> track it down for debugging!
Sometimes, I do want side effects! What if I know that every time I
call "squareMe" I will want to modify the var. being squared?
I'd rather write:
squareMe $n
than
$n = squareMe $n
------------------------------
Date: Thu, 09 Aug 2007 19:27:08 GMT
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: pass by reference
Message-Id: <x7k5s4jypc.fsf@mail.sysarch.com>
>>>>> "L" == Larry <larry.grant.dc@gmail.com> writes:
L> On Aug 9, 2:59 pm, Uri Guttman <u...@stemsystems.com> wrote:
>> >>>>> "L" == Larry <larry.grant...@gmail.com> writes:
>>
L> I don't like the $_[0] method, because it doesn't give me a chance to
L> name my variables.... I prefer names, not numbers, thank you! :)
>>
>> so pass in a reference. the typeglob hack you created is fugly and
>> wasteful. and don't use prototypes as they are not what you want here. a
>> plain simple reference works fine.
>>
L> I don't want to pass in a reference! You call that "passing by
L> reference"?! :)
sure is but it is just explicit. i know what pass by ref is.
L> I want to write:
L> squareMe $foo
L> not
L> squareMe \$foo
well, then use $_[0] as others have said. your typeglob answer is
horrible for such a simple issue. in my view you are working too hard
for a tiny syntactical gain. this is from a few weeks of coding
experience that i have :)
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org
------------------------------
Date: Thu, 09 Aug 2007 19:28:06 GMT
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: pass by reference
Message-Id: <x7fy2sjynp.fsf@mail.sysarch.com>
>>>>> "L" == Larry <larry.grant.dc@gmail.com> writes:
L> On Aug 9, 3:07 pm, Larry <larry.grant...@gmail.com> wrote:
>> On Aug 9, 2:59 pm, Uri Guttman <u...@stemsystems.com> wrote:
>>
>> > >>>>> "L" == Larry <larry.grant...@gmail.com> writes:
>>
>> > L> I don't like the $_[0] method, because it doesn't give me a chance to
>> > L> name my variables.... I prefer names, not numbers, thank you! :)
>>
>> > so pass in a reference. the typeglob hack you created is fugly and
>> > wasteful. and don't use prototypes as they are not what you want here. a
>> > plain simple reference works fine.
>>
>> I don't want to pass in a reference! You call that "passing by
>> reference"?! :)
>>
>> I want to write:
>>
>> squareMe $foo
>>
>> not
>>
>> squareMe \$foo
>>
>> !!!
L> And I *do* need the prototypes... that's the only way to get the
L> reference without my callers having to use backslashes!
nope again. they can get a ref earlier into another scalar and pass
that. your api design to make their life 'easier' is actually making it
harder. but do what you want.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org
------------------------------
Date: Thu, 09 Aug 2007 19:29:07 GMT
From: Uri Guttman <uri@stemsystems.com>
Subject: Re: pass by reference
Message-Id: <x7bqdgjym1.fsf@mail.sysarch.com>
>>>>> "L" == Larry <larry.grant.dc@gmail.com> writes:
L> On Aug 9, 1:50 pm, Larry <larry.grant...@gmail.com> wrote:
>> The following code snippet shows how I do "pass by reference" in
>> Perl. It works fine, but I'm wondering... is there a less verbose way
>> to do this?
>>
>> (I know in this simple example, I could avoid the typeglob assignment
>> and just use $$arg instead of $arg, but in a more complex usage, that
>> would bug me... I'd rather just use the more normal-looking $arg
>> everywhere.)
>>
>> -------------
>>
>> sub squareMe (\$) {
>> my ($argRef) = @_;
>> local *arg = $argRef;
>> our $arg;
>>
>> $arg *= $arg;
>>
>> }
>>
>> my $n = 7;
>> squareMe $n;
>> print "$n\n"; # prints 49
L> I just figured out a somewhat more elegant way:
L> sub squareMe (\$) {
L> local (*arg) = @_;
L> our $arg;
L> $arg *= $arg;
L> }
ewwwwww!
L> Too bad about the need for having to repeat "arg" in "our" though...
double ewwwwww.
tell them to pass a real ref and be done with it. they need to learn
about refs anyhow and coddling your callers is doing them a big
disservice.
uri
--
Uri Guttman ------ uri@stemsystems.com -------- http://www.stemsystems.com
--Perl Consulting, Stem Development, Systems Architecture, Design and Coding-
Search or Offer Perl Jobs ---------------------------- http://jobs.perl.org
------------------------------
Date: Thu, 09 Aug 2007 19:39:36 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186688376.999386.300820@g12g2000prg.googlegroups.com>
> tell them to pass a real ref and be done with it. they need to learn
> about refs anyhow and coddling your callers is doing them a big
> disservice.
>
> uri
I see your point, but I miss "real" passing by reference from Pascal
and Ada. But C, Perl and Java seem to want to bury it :(
------------------------------
Date: Thu, 09 Aug 2007 19:40:49 -0000
From: Larry <larry.grant.dc@gmail.com>
Subject: Re: pass by reference
Message-Id: <1186688449.373686.21240@i38g2000prf.googlegroups.com>
On Aug 9, 3:39 pm, Larry <larry.grant...@gmail.com> wrote:
> > tell them to pass a real ref and be done with it. they need to learn
> > about refs anyhow and coddling your callers is doing them a big
> > disservice.
>
> > uri
>
> I see your point, but I miss "real" passing by reference from Pascal
> and Ada. But C, Perl and Java seem to want to bury it :(
And put C++ in with Pascal and Ada!
------------------------------
Date: Thu, 09 Aug 2007 14:06:40 -0500
From: "J. Gleixner" <glex_no-spam@qwest-spam-no.invalid>
Subject: Re: Replacing a line
Message-Id: <46bb65c0$0$3572$815e3792@news.qwest.net>
Ved wrote:
> On Aug 7, 3:17 am, "J. Gleixner" <glex_no-s...@qwest-spam-no.invalid>
> wrote:
>> Ved wrote:
>>> Hi all,
>>> I have to replace commented line in a list of " .cpp" file .
>>> Line looks like this:
>>> //#define BBPRxChanRouteFileLoadInput 1
>>> i.e. The line format :
>>> //#define (FileName)FileLoadInput 1
>>> is to be replaced with
>>> #define (FileName)FileLoadInput 1
[...]
>> for( @array )
>> {
>> # Need to escape the $
>> if( m{^//#define \$dirFileLoadInput 1$} )
>> {
>> s{^//}{};
>> last;
>> }
>> }
>>
>> Documentation on regular expressions:
>>
>> perldoc perlretut
> Hi Gleixner,
>
> Why is it not entering in this condition ?
>
> if( m{^//#define \$module_nameFileLoadInput 1$} )
>
Sorry, my fault. I misssed that $dir was a variable, in
your match. For some reason I thought you were trying to
actually match a string that contained '$dirFileLoadInput'.
${module_name}FileLoadInput
------------------------------
Date: Thu, 09 Aug 2007 18:46:32 GMT
From: "John W. Krahn" <dummy@example.com>
Subject: Re: Size of all files in a directory?
Message-Id: <ciJui.83080$tB5.1320@edtnps90>
Paul Lalli wrote:
> On Aug 9, 8:14 am, Paul Lalli <mri...@gmail.com> wrote:
>> On Aug 9, 1:08 am, "comp.llang.perl.moderated" <c...@blv-
>> sam-01.ca.boeing.com> wrote:
>>> On Aug 7, 3:20 pm, Paul Lalli <mri...@gmail.com> wrote:
>>>> there's nothing intuitively telling me readdir returned
>>>> false because there was an OS error, or because the
>>>> directory actually was empty. I guess I would rather it
>>>> throw an exception.
>>> You could get something very similar with Fatal's "succeed
>>> or die" semantics:
>> Interesting, I hadn't considered that. Thanks for the idea.
>
> Uhm, I conditionally take that back. ;-) Fatal seems to severely
> FUBAR readdir(). What am I doing wrong?
$ perl -wle'
use Fatal qw/readdir/;
opendir DH, "." or die $!;
my @files = readdir DH;
print for @files;
'
Name "main::DH" used only once: possible typo at -e line 3.
test
It appears that the directory handle is invalidated at some point?
John
--
Perl isn't a toolbox, but a small machine shop where you
can special-order certain sorts of tools at low cost and
in short order. -- Larry Wall
------------------------------
Date: 6 Apr 2001 21:33:47 GMT (Last modified)
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------------------------------
End of Perl-Users Digest V11 Issue 737
**************************************
