Clarification on the use of "my"

Just a quick question on the need of "my" http://perldoc.perl.org/functions/my.html

Was using an example from the beginning perl text in the example he
gave he wasn't using strict but i have it on to all scripts by
default.

For this example. the first two assignments work okay, but then at $c
if I do not declare my local then I get an error. $d also requires
that it be assigned using my, though it is directly the same as $b, my
assumption here is that $d required explicit assignment as it used the
explicitly assigned variable $c (could be wrong).

Why from $c was "my" required?
NB I am using 5.14.1

#!/usr/bin/perl -w
# vars3.pl --- Assignment of vars using strict
# Author: sayth
# Created: 05 Sep 2011
# Version: 0.01

use warnings;
use strict;

$a = 6*9;
print "six times 9 is ", $a, "\n";
$b = $a + 3;
print "plus three is ", $b,"\n";
my $c = $b/3;
print "Divided by 3 is ", $c, "\n";
my $d = $c + 1;
print "plus one is ", $d, "\n";


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Re: Clarification on the use of "my"

On Sun, Sep 4, 2011 at 11:53 PM, flebber wrote:
> For this example. the first two assignments work okay, but then at $c
> if I do not declare my local then I get an error. $d also requires
> that it be assigned using my, though it is directly the same as $b, my
> assumption here is that $d required explicit assignment as it used the
> explicitly assigned variable $c (could be wrong).
>
> Why from $c was "my" required?
*snip*
> $a = 6*9;
> print "six times 9 is ", $a, "\n";
> $b = $a + 3;
> print "plus three is ", $b,"\n";
> my $c = $b/3;
> print "Divided by 3 is ", $c, "\n";
> my $d = $c + 1;
> print "plus one is ", $d, "\n";

$a and $b are special global variables used by sort. :) See perldoc
perlvar and/or perldoc -f sort. :) So, in short, $a and $b already
existed, so there was no problem using them without declaring them
first. You should ALWAYS declare your variables. :) You either use
'my' for a lexical scope or 'our' for module scope. :) There is also
'local', but I'm not going to attempt to explain how that works so
early in the morning. You should be able to learn about each using
perldoc -f though. To be safe and clear you shouldn't use the names $a
and $b unless you are actually using them within a sort.


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Re: Clarification on the use of "my"

>>>>> "BM" == Brandon McCaig writes:

BM> On Sun, Sep 4, 2011 at 11:53 PM, flebber wrote:
>> For this example. the first two assignments work okay, but then at $c
>> if I do not declare my local then I get an error. $d also requires
>> that it be assigned using my, though it is directly the same as $b, my
>> assumption here is that $d required explicit assignment as it used the
>> explicitly assigned variable $c (could be wrong).
>>
>> Why from $c was "my" required?
BM> *snip*
>> $a = 6*9;
>> print "six times 9 is ", $a, "\n";
>> $b = $a + 3;
>> print "plus three is ", $b,"\n";
>> my $c = $b/3;
>> print "Divided by 3 is ", $c, "\n";
>> my $d = $c + 1;
>> print "plus one is ", $d, "\n";

BM> $a and $b are special global variables used by sort. :) See perldoc
BM> perlvar and/or perldoc -f sort. :) So, in short, $a and $b already
BM> existed, so there was no problem using them without declaring them
BM> first. You should ALWAYS declare your variables. :) You either use
BM> 'my' for a lexical scope or 'our' for module scope. :) There is also

there is no such thing as module scope. our declares package globals and
give them a short name in a lexical scope.

BM> 'local', but I'm not going to attempt to explain how that works so
BM> early in the morning. You should be able to learn about each using
BM> perldoc -f though. To be safe and clear you shouldn't use the names $a
BM> and $b unless you are actually using them within a sort.

single letter variable names are bad in general. they tell you nothing
about the use and content of the variable. about the only exception are
$i and $j for array/matrix indexing and the aforementioned $a and $b for
scoping.

uri

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Re: Clarification on the use of "my"

On Mon, Sep 5, 2011 at 11:51 AM, Uri Guttman wrote:
> there is no such thing as module scope. our declares package globals and
> give them a short name in a lexical scope.

Ah, yes, thank you for correcting me. :) The line between "module" and
"package" had blurred on me. Google cleared that up.

> single letter variable names are bad in general. they tell you nothing
> about the use and content of the variable. about the only exception are
> $i and $j for array/matrix indexing and the aforementioned $a and $b for
> scoping.

I'm used to writing C# and in my experience descriptive variable names
become both tiresome and difficult to read. Instead, I usually try to
keep functions/subroutines short and give variable names a mnemonic
meaning. If it is not obvious what the variable's purpose is then I'll
leave a comment next to its declaration (often in C# the type alone
describes the variable sufficiently though). I do use descriptive
names when the code requires it, but I don't make it a rule to always
use them. I find that code is often more difficult to read when the
names exceed a few characters. It's important to see what a variable
represents, but it's also important to see how that variable interacts
with the code around it.

This habit is somewhat holstered due to Perl's use of global variables
with short names, like $a and $b. I don't remember if there are any
other /\$[A-za-z]/ variables, but to be safe I generally avoid using
single character names in Perl (well, OK, also to avoid getting "told"
on this list when I post my code). I guess variable name length is
less of an issue in Perl though because the language is so much more
terse all by itself :P


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Re: Clarification on the use of "my"

>>>>> "BM" == Brandon McCaig writes:

BM> On Mon, Sep 5, 2011 at 11:51 AM, Uri Guttman wrote:

>> single letter variable names are bad in general. they tell you nothing
>> about the use and content of the variable. about the only exception are
>> $i and $j for array/matrix indexing and the aforementioned $a and $b for
>> scoping.

BM> I'm used to writing C# and in my experience descriptive variable names
BM> become both tiresome and difficult to read. Instead, I usually try to
BM> keep functions/subroutines short and give variable names a mnemonic
BM> meaning. If it is not obvious what the variable's purpose is then I'll
BM> leave a comment next to its declaration (often in C# the type alone
BM> describes the variable sufficiently though). I do use descriptive
BM> names when the code requires it, but I don't make it a rule to always
BM> use them. I find that code is often more difficult to read when the
BM> names exceed a few characters. It's important to see what a variable
BM> represents, but it's also important to see how that variable interacts
BM> with the code around it.

it doesn't matter the language or the comments. single letter var names
are just bad coding. names are a communication to the reader of the
code, not a placeholder or whatever to the coder. much more work needs
to be put into choosing good names than most coders realize. it is one
of the major characteristics i look for when i review code (and i review
a ton of code for my business of place perl hackers).

BM> This habit is somewhat holstered due to Perl's use of global variables
BM> with short names, like $a and $b. I don't remember if there are any
BM> other /\$[A-za-z]/ variables, but to be safe I generally avoid using
BM> single character names in Perl (well, OK, also to avoid getting "told"
BM> on this list when I post my code). I guess variable name length is
BM> less of an issue in Perl though because the language is so much more
BM> terse all by itself :P

as i said, name quality is independent of language choice. $a and $b are
special cases only for sort and nowhere else are any special named
variables are found in perl (other than the punctuation vars like $!).

uri

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Re: Clarification on the use of "my"

On Mon, Sep 5, 2011 at 2:54 PM, Uri Guttman wrote:
> it doesn't matter the language or the comments. single letter var names
> are just bad coding. names are a communication to the reader of the
> code, not a placeholder or whatever to the coder. much more work needs
> to be put into choosing good names than most coders realize. it is one
> of the major characteristics i look for when i review code (and i review
> a ton of code for my business of place perl hackers).

You're welcome to your opinion.


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Re: Clarification on the use of "my"

>>>>> "BM" == Brandon McCaig writes:

BM> On Mon, Sep 5, 2011 at 2:54 PM, Uri Guttman wrote:
>> it doesn't matter the language or the comments. single letter var names
>> are just bad coding. names are a communication to the reader of the
>> code, not a placeholder or whatever to the coder. much more work needs
>> to be put into choosing good names than most coders realize. it is one
>> of the major characteristics i look for when i review code (and i review
>> a ton of code for my business of place perl hackers).

BM> You're welcome to your opinion.

it isn't just mine. and since i have been coding for 37 years, done
training, review code for placements and more, my opinion carries a
little weight with those who know me. you may not agree but that puts
you on the side of not appreciating what code quality means. i can see i
won't be helping you with any perl jobs in the future as that is an
attitude i can't support.

just to clarify, here are the rules simple enough for anyone to
understand.

code is for people, not computers.

code is for other people, not yourself.

think about those for a bit or a few years maybe. they will eventually
ring true to you.

uri

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Re: Clarification on the use of "my"

On 05/09/2011 16:51, Uri Guttman wrote:
>
> there is no such thing as module scope. our declares package globals and
> give them a short name in a lexical scope.

All software comcepts exist only in someone's imagination. Brandon and I
can imagine what 'module scope' means and I am surprised that you
cannot. In the end there are only global declarations and scoped
declarations, and I believe you are wrong to pick holes in people's
terminology when it is quite clear what they mean, and that meaning is
correct.

> BM> 'local', but I'm not going to attempt to explain how that works so
> BM> early in the morning. You should be able to learn about each using
> BM> perldoc -f though. To be safe and clear you shouldn't use the names $a
> BM> and $b unless you are actually using them within a sort.
>
> single letter variable names are bad in general. they tell you nothing
> about the use and content of the variable. about the only exception are
> $i and $j for array/matrix indexing and the aforementioned $a and $b for
> scoping.

Fortran tradition has us use 'i' .. 'n' for integer values - often
counters - and everything else for floats, of which 'x' .. 'z' are
familiar in mathematical and graphical programming. Outside that, qw/Y M
D h m s/ are universal, $c is an undimensioned constant, $e is exp(1),
$f is a file or a format, $g is the gravitational constant, $h would be
height, hours, Henries, and so on.

I know I have said something very similar before, but those who disagree
with me are forgetting Perl's legacy. It is a language that is intended
to cope with ambiguity by context, and can tell the difference between
the equivalents of there, their and they're; and even its, it's and it's.

So yes, we are free to use single-character variable names if that use
is unambiguous in context. Unfortunately most people have a history of
writing software that looks like bricklaying: every stroke and placement
has its own independent purpose. So we get C programmers, Fortran
programmers, and possibly COBOL programmers, each writing Perl code
where every single line will stand unambiguously on its own. That is not
what Perl is for, and it goes a long way to explaining the controversy
that it generates.

The reason $a and $b are broken is because of a fix on top of a nice
idea. There should be nothing wrong with names like that but, because no
one thought of it sooner, it can be a better rule to prohibit
single-character variable names altogether.

My rule would be to write what you mean, all of the time. If for some
defect in the language that doesn't work, then understand why and write
what you mean in a different way. People will love you for it.

Rob

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Re: Clarification on the use of "my"

On 05/09/2011 19:54, Uri Guttman wrote:
>
> it doesn't matter the language or the comments. single letter var names
> are just bad coding. names are a communication to the reader of the
> code, not a placeholder or whatever to the coder. much more work needs
> to be put into choosing good names than most coders realize. it is one
> of the major characteristics i look for when i review code (and i review
> a ton of code for my business of place perl hackers).

I would counter with the thought that lack of capitalisation is just
poor-quality and bad-mannered writing. Capitals provide a focus for the
reader to understand the meaning of what has been written without having
to examine every word, just as the serifs on a properly-chosen body text
font lead the reader to the next symbol.

Much more work should be put into your literary style than you realise,
as your documentation and comments will be your sole means of
communication to all who have site of your code while you are not there
to explain it.

I am certain that no one who is unable to format and punctuate their own
written language properly can possibly imagine how to write software
that is both functional and comprehensible.

Rob

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Re: Clarification on the use of "my"

On 05/09/2011 21:26, Uri Guttman wrote:
>
> off list
>
> rob,

No. This order of nastiness cannot be done in private. Your words are
crude and brutal, and backed by no one here.

ON list.

> what is with your attitude recently? you had that blowup a few months
> ago. are you doing that again? i really think you should take a breather
> here and get your head clear. i am just concerned about your tone here
> right now. i haven't been nasty or anything in my recent posts but you
> are getting personal for no apparent reason. cool it off please.

If you look back at the archives, I explained 'that blowup' and
apologised for it. Things are different now, and despite our situation
we are doing well and improving. Your references to my daughter don't
help what I am trying to do, and to me they seem rude and inconsiderate.

I wonder why you have started belittling the questions here instead of
offering a useful answer. I believe it is for you as an intelligent Perl
programmer to reply constructively to questions posed here. All we have
seen rudeness that will discourage any questiond at all.

Please go think again Uri.

Rob







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Re: Clarification on the use of "my"

>>>>> "RD" == Rob Dixon writes:

RD> On 05/09/2011 21:26, Uri Guttman wrote:
>>
>> off list
>>
>> rob,

RD> No. This order of nastiness cannot be done in private. Your words are
RD> crude and brutal, and backed by no one here.

RD> ON list.

>> what is with your attitude recently? you had that blowup a few months
>> ago. are you doing that again? i really think you should take a breather
>> here and get your head clear. i am just concerned about your tone here
>> right now. i haven't been nasty or anything in my recent posts but you
>> are getting personal for no apparent reason. cool it off please.

RD> If you look back at the archives, I explained 'that blowup' and
RD> apologised for it. Things are different now, and despite our situation
RD> we are doing well and improving. Your references to my daughter don't
RD> help what I am trying to do, and to me they seem rude and inconsiderate.

what reference to what daughter? i didn't know about or care about your
family.

RD> I wonder why you have started belittling the questions here instead of
RD> offering a useful answer. I believe it is for you as an intelligent Perl
RD> programmer to reply constructively to questions posed here. All we have
RD> seen rudeness that will discourage any questiond at all.

again, what are you talking about? i made some feedback on some post as
usual. the OP didn't object nor did anyone else, just you. the last time
i did something (i upper cased NEVER) it caused a silly firestorm and
nothing like that happened this time. you just jumped on my comments and
no one else did.

uri

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Re: Clarification on the use of "my"

>>>>> "Rob" == Rob Dixon writes:

Rob> All software comcepts exist only in someone's imagination. Brandon and I
Rob> can imagine what 'module scope' means and I am surprised that you
Rob> cannot. In the end there are only global declarations and scoped
Rob> declarations, and I believe you are wrong to pick holes in people's
Rob> terminology when it is quite clear what they mean, and that meaning is
Rob> correct.

I can imagine what a module scope might be, and what "our" does isn't
it. So there's the problem. We imagine different things for that word,
and then we have no authority to define it.

That's *why* you should use the *proper* words. No communication
without that.

For the record, "my" and "our" have *precisely* the same scoping
rules. The variable name they introduce has different bindings, however.

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Re: Clarification on the use of "my"

>>>>> "Rob" == Rob Dixon writes:

Rob> No. This order of nastiness cannot be done in private. Your words are crude
Rob> and brutal, and backed by no one here.

Rob> ON list.

[presumably private message made public deleted]

*NOW* you've violated a very fundamental rule of mailing list etiquette.

You should never ever bring someone's *private* email into a *public*
list without their permission, no matter how hurt you feel.

Whatever support you might have gotten from me regarding the issue
is now *gone*. Is that clear?

Methinks you should *now* do what I *must* do from time to time here...

.... and take a break. please.

go away for a bit. chill out.

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Re: Clarification on the use of "my"

On 16/09/2011 23:43, Randal L. Schwartz wrote:
>>>>>> "Rob" == Rob Dixon writes:
>
> Rob> No. This order of nastiness cannot be done in private. Your words are crude
> Rob> and brutal, and backed by no one here.
>
> Rob> ON list.
>
> [presumably private message made public deleted]
>
> *NOW* you've violated a very fundamental rule of mailing list etiquette.
>
> You should never ever bring someone's *private* email into a *public*
> list without their permission, no matter how hurt you feel.
>
> Whatever support you might have gotten from me regarding the issue
> is now *gone*. Is that clear?
>
> Methinks you should *now* do what I *must* do from time to time here...
>
> ... and take a break. please.
>
> go away for a bit. chill out.

I hoped to hear about this from the less elite on the group.

Uri has said a very similar thing about me on list, and there was plenty
of opportunity there for you to express 'whatever support' you wanted.

My contravention of your 'fundamental rules' shouldn't stop you
expressing your thoughts, whether or not they support what you see as my
position.

Scattering asterisks and upper case about your post seems rather silly
to me. Certainly, "Is that clear?" is rhetorical and very rude, and it
all suggests that you should be taking your own advice here.

You and Uri are amongst those who see themselves as the elite of the
Perl community. All that either of you have shown me is that you are
rather fond of yourselves and like to see your opinions as lore.

I am no japh - that has become a label for anti-snobbery - I am a Perl
programmer who likes to understand his craft, perform it well, and pass
on what he knows to others. I am also grateful that I am able to teach
well, and can pass on my ideas together with the notion that there are
always alternative solutions that I have not come across.

Randal, from your posts here and your public history I worry that you
lack humility and require that your assertions be accepted as truth. Uri
seems to behave similarly, and both of you hide behind the defence (that
I believe you invented) that you attack not the person but their behaviour.

This being a First-World, Western, Capitalist list, I invite both you
(Randal) and Uri to exemplify the difference between a person and his
behaviour.

In the mean time, to Uri, I am sure the majority of us here would rather
you stopped flexing your experience muscles at us and started to help us
become the Perl programmers that we could be. It is embarrassing that
you promote yourself and your CPAN modules here above everything else
available, and if there is one regular poster to this list who is
insecure and identifies themselves with their achievements then it is you.

A final thought to Randal. I think you are right that I shouldn't have
publicized a private mail from Uri. In my defence, this is a list where
rules are different: we try incessantly to get people who post here to
edit the post they are replying to and add their response afterwards;
the majority will be used to doing the opposite in casual or business
mail. We are also often replied to personally - either by mistake or
because of ignorance - and force that reply back to the relevant thread
on this list.

That said, I am aware that some of my posts may have been out of order a
while ago, and I explained and apologised at the time. I hoped that
would be the end of it until Uri saw it as a hit on his unblemished record.

> [My opinion] isn't just mine. and since i have been coding for 37
> years, done training, review code for placements and more, my
> opinion carries a little weight with those who know me. you may not
> agree but that puts you on the side of not appreciating what code
> quality means. i can see i won't be helping you with any perl jobs in
> the future as that is an attitude i can't support.

In my experience, bigness in business is more likely to encourage egoes
than good programming.

Rob

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