common-sense/sense.pm

=head1 NAME

common::sense - save a tree AND a kitten, use common::sense!

=head1 SYNOPSIS

 use common::sense;

 # supposed to be the same, with much lower memory usage, as:
 #
 # use strict qw(vars subs);
 # use feature qw(say state switch);
 # no warnings;
 # use warnings qw(FATAL closed threads internal debugging pack substr malloc
 #                 unopened portable prototype inplace io pipe unpack regexp
 #                 deprecated exiting glob digit printf utf8 layer
 #                 reserved parenthesis taint closure semicolon);
 # no warnings qw(exec newline);

=head1 DESCRIPTION

This module implements some sane defaults for Perl programs, as defined by
two typical (or not so typical - use your common sense) specimens of Perl
coders. In fact, after working out details on which warnings and strict
modes to enable and make fatal, we found that we (and our code written so
far, and others) fully agree on every option, even though we never used
warnings before, so it seems this module indeed reflects a "common" sense
among some long-time Perl coders.

=over 4

=item use strict qw(subs vars)

Using C<use strict> is definitely common sense, but C<use strict
'refs'> definitely overshoots its usefulness. After almost two
decades of Perl hacking, we decided that it does more harm than being
useful. Specifically, constructs like these:

   @{ $var->[0] }

Must be written like this (or similarly), when C<use strict 'refs'> is in
scope, and C<$var> can legally be C<undef>:

   @{ $var->[0] || [] }

This is annoying, and doesn't shield against obvious mistakes such as
using C<"">, so one would even have to write (at least for the time
being):

   @{ defined $var->[0] ? $var->[0] : [] }

... which nobody with a bit of common sense would consider
writing: clear code is clearly something else.

Curiously enough, sometimes perl is not so strict, as this works even with
C<use strict> in scope:

   for (@{ $var->[0] }) { ...

If that isn't hypocrisy! And all that from a mere program!


=item use feature qw(say state given)

We found it annoying that we always have to enable extra features. If
something breaks because it didn't anticipate future changes, so be
it. 5.10 broke almost all our XS modules and nobody cared either (or at
least I know of nobody who really complained about gratuitous changes -
as opposed to bugs).

Few modules that are not actively maintained work with newer versions of
Perl, regardless of use feature or not, so a new major perl release means
changes to many modules - new keywords are just the tip of the iceberg.

If your code isn't alive, it's dead, Jim - be an active maintainer.


=item no warnings, but a lot of new errors

Ah, the dreaded warnings. Even worse, the horribly dreaded C<-w>
switch: Even though we don't care if other people use warnings (and
certainly there are useful ones), a lot of warnings simply go against the
spirit of Perl.

Most prominently, the warnings related to C<undef>. There is nothing wrong
with C<undef>: it has well-defined semantics, it is useful, and spitting
out warnings you never asked for is just evil.

The result was that every one of our modules did C<no warnings> in the
past, to avoid somebody accidentally using and forcing his bad standards
on our code. Of course, this switched off all warnings, even the useful
ones. Not a good situation. Really, the C<-w> switch should only enable
warnings for the main program only.

Funnily enough, L<perllexwarn> explicitly mentions C<-w> (and not in a
favourable way, calling it outright "wrong"), but standard utilities, such
as L<prove>, or MakeMaker when running C<make test>, still enable them
blindly.

For version 2 of common::sense, we finally sat down a few hours and went
through I<every single warning message>, identifiying - according to
common sense - all the useful ones.

This resulted in the rather impressive list in the SYNOPSIS. When we
weren't sure, we didn't include the warning, so the list might grow in
the future (we might have made a mistake, too, so the list might shrink
as well).

Note the presence of C<FATAL> in the list: we do not think that the
conditions caught by these warnings are worthy of a warning, we I<insist>
that they are worthy of I<stopping> your program, I<instantly>. They are
I<bugs>!

Therefore we consider C<common::sense> to be much stricter than C<use
warnings>, which is good if you are into strict things (we are not,
actually, but these things tend to be subjective).

After deciding on the list, we ran the module against all of our code that
uses C<common::sense> (that is almost all of our code), and found only one
occurence where one of them caused a problem: one of elmex's (unreleased)
modules contained:

   $fmt =~ s/([^\s\[]*)\[( [^\]]* )\]/\x0$1\x1$2\x0/xgo;

We quickly agreed that indeed the code should be changed, even though it
happened to do the right thing when the warning was switched off.


=item mucho reduced memory usage

Just using all those pragmas mentioned in the SYNOPSIS together wastes
<blink>I<< B<776> kilobytes >></blink> of precious memory in my perl, for
I<every single perl process using our code>, which on our machines, is a
lot. In comparison, this module only uses I<< B<four> >> kilobytes (I even
had to write it out so it looks like more) of memory on the same platform.

The money/time/effort/electricity invested in these gigabytes (probably
petabytes globally!) of wasted memory could easily save 42 trees, and a
kitten!

Unfortunately, until everybods applies more common sense, there will still
often be modules that pull in the monster pragmas. But one can hope...

=cut

package common::sense;

our $VERSION = '2.01';

# paste this into perl to find bitmask

# no warnings;
# use warnings qw(FATAL closed threads internal debugging pack substr malloc unopened portable prototype
#                 inplace io pipe unpack regexp deprecated exiting glob digit printf
#                 utf8 layer reserved parenthesis taint closure semicolon);
# no warnings qw(exec newline);
# BEGIN { warn join "", map "\\x$_", unpack "(H2)*", ${^WARNING_BITS}; exit 0 };

# overload should be included

sub import {
   # verified with perl 5.8.0, 5.10.0
   ${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\xfc\x3f\xf3\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";

   # use strict vars subs
   $^H |= 0x00000600;

   # use feature
   $^H{feature_switch} =
   $^H{feature_say}    =
   $^H{feature_state}  = 1;
}

1;

=back

=head1 THERE IS NO 'no common::sense'!!!! !!!! !!

This module doesn't offer an unimport. First of all, it wastes even more
memory, second, and more importantly, who with even a bit of common sense
would want no common sense?

=head1 STABILITY AND FUTURE VERSIONS

Future versions might change just about everything in this module. We
might test our modules and upload new ones working with newer versions of
this module, and leave you standing in the rain because we didn't tell
you. In fact, we did so when switching from 1.0 to 2.0, which enabled gobs
of warnings, and made them FATAL on top.

Maybe we will load some nifty modules that try to emulate C<say> or so
with perls older than 5.10 (this module, of course, should work with older
perl versions - supporting 5.8 for example is just common sense at this
time. Maybe not in the future, but of course you can trust our common
sense to be consistent with, uhm, our opinion).

=head1 WHAT OTHER PEOPLE HAD TO SAY ABOUT THIS MODULE

apeiron

   "... wow"
   "I hope common::sense is a joke."

crab

   "i wonder how it would be if joerg schilling wrote perl modules."

Adam Kennedy

   "Very interesting, efficient, and potentially something I'd use all the time."
   [...]
   "So no common::sense for me, alas."

H.Merijn Brand

   "Just one more reason to drop JSON::XS from my distribution list"

Pista Palo

   "Something in short supply these days..."

Steffen Schwigon

   "This module is quite for sure *not* just a repetition of all the other
   'use strict, use warnings'-approaches, and it's also not the opposite.
   [...] And for its chosen middle-way it's also not the worst name ever.
   And everything is documented."

BKB

   "[Deleted - thanks to Steffen Schwigon for pointing out this review was
   in error.]"

Somni

   "the arrogance of the guy"
   "I swear he tacked somenoe else's name onto the module
   just so he could use the royal 'we' in the documentation"

dngor

   "Heh.  '"<elmex at ta-sa.org>"'  The quotes are semantic
   distancing from that e-mail address."

Jerad Pierce

   "Awful name (not a proper pragma), and the SYNOPSIS doesn't tell you
   anything either. Nor is it clear what features have to do with "common
   sense" or discipline."

acme

   "THERE IS NO 'no common::sense'!!!! !!!! !!"

apeiron (meta-comment about us commenting^Wquoting his comment)

   How about quoting this: get a clue, you fucktarded amoeba.

quanth

   common sense is beautiful, json::xs is fast, Anyevent, EV are fast and
   furious. I love mlehmannware ;)

=head1 FREQUQNTLY ASKED QUESTIONS

Or frequently-come-up confusions.

=over 4

=item Is this module meant to be serious?

Yes, we would have put it under the C<Acme::> namespace otherwise.

=item But the manpage is written in a funny/stupid/... way?

This was meant to make it clear that our common sense is a subjective
thing and other people can use their own notions, taking the steam out
of anybody who might be offended (as some people are always offended no
matter what you do).

This was a failure.

But we hope the manpage still is somewhat entertaining even though it
explains boring rationale.

=item Why do you impose your conventions on my code?

For some reason people keep thinking that C<common::sense> imposes
process-wide limits, even though the SYNOPSIS makes it clear that it works
like other similar modules - only on the scope that uses them.

So, no, we don't - nobody is forced to use this module, and using a module
that relies on common::sense does not impose anything on you.

=item Why do you think only your notion of common::sense is valid?

Well, we don't, and have clearly written this in the documentation to
every single release. We were just faster than anybody else w.r.t. to
grabbing the namespace.

=item But everybody knows that you have to use strict and use warnings,
why do you disable them?

Well, we don't do this either - we selectively disagree with the
usefulness of some warnings over others. This module is aimed at
experienced Perl programmers, not people migrating from other languages
who might be surprised about stuff such as C<undef>.

In fact, this module is considerably I<more> strict than the canonical
C<use strict; use warnings>, as it makes all warnings fatal in nature, so
you can get away with as many things as with the canonical approach.

This was not implemented in version 1.0 because of the daunting number
of warning categories and the difficulty in getting exactly the set of
warnings you wish (i.e. look at the SYNOPSIS in how complicated it is to
get a specific set of warnings - it is not reasonable to put this into
every module, the maintainance effort would be enourmous).

=item But many modules C<use strict> or C<use warnings>, so the memory
savings do not apply?

I am suddenly so sad.

But yes, that's true. Fortunately C<common::sense> still uses only a
miniscule amount of RAM.

=item But it adds another dependency to your modules!

It's a fact, yeah. But it's trivial to install, most popular modules have
many more dependencies and we consider dependencies a good thing - it
leads to better APIs, more thought about interworking of modules and so
on.

=item But! But!

Yeah, we know.

=back

=head1 AUTHOR

 Marc Lehmann <schmorp@schmorp.de>
 http://home.schmorp.de/

 Robin Redeker, "<elmex at ta-sa.org>".

=cut

Revision:	1.21
Committed:	Fri Oct 30 02:58:05 2009 UTC (14 years, 8 months ago) by root
Branch:	MAIN
Changes since 1.20:	+5 -1 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			common::sense - save a tree AND a kitten, use common::sense!
4
5			=head1 SYNOPSIS
6
7			use common::sense;
8
9	root	1.19	# supposed to be the same, with much lower memory usage, as:
10	root	1.1	#
11			# use strict qw(vars subs);
12			# use feature qw(say state switch);
13			# no warnings;
14	root	1.15	# use warnings qw(FATAL closed threads internal debugging pack substr malloc
15			# unopened portable prototype inplace io pipe unpack regexp
16	root	1.16	# deprecated exiting glob digit printf utf8 layer
17	root	1.15	# reserved parenthesis taint closure semicolon);
18			# no warnings qw(exec newline);
19	root	1.1
20			=head1 DESCRIPTION
21
22			This module implements some sane defaults for Perl programs, as defined by
23	root	1.16	two typical (or not so typical - use your common sense) specimens of Perl
24	root	1.21	coders. In fact, after working out details on which warnings and strict
25			modes to enable and make fatal, we found that we (and our code written so
26			far, and others) fully agree on every option, even though we never used
27			warnings before, so it seems this module indeed reflects a "common" sense
28			among some long-time Perl coders.
29	root	1.1
30			=over 4
31
32			=item use strict qw(subs vars)
33
34			Using C<use strict> is definitely common sense, but C<use strict
35	root	1.11	'refs'> definitely overshoots its usefulness. After almost two
36	root	1.1	decades of Perl hacking, we decided that it does more harm than being
37			useful. Specifically, constructs like these:
38
39			@{ $var->[0] }
40
41	root	1.4	Must be written like this (or similarly), when C<use strict 'refs'> is in
42			scope, and C<$var> can legally be C<undef>:
43	root	1.1
44			@{ $var->[0] \|\| [] }
45
46			This is annoying, and doesn't shield against obvious mistakes such as
47	root	1.11	using C<"">, so one would even have to write (at least for the time
48			being):
49	root	1.1
50	root	1.18	@{ defined $var->[0] ? $var->[0] : [] }
51	root	1.1
52			... which nobody with a bit of common sense would consider
53	root	1.18	writing: clear code is clearly something else.
54	root	1.11
55			Curiously enough, sometimes perl is not so strict, as this works even with
56			C<use strict> in scope:
57	root	1.1
58			for (@{ $var->[0] }) { ...
59
60	root	1.15	If that isn't hypocrisy! And all that from a mere program!
61
62	root	1.1
63			=item use feature qw(say state given)
64
65			We found it annoying that we always have to enable extra features. If
66			something breaks because it didn't anticipate future changes, so be
67	root	1.11	it. 5.10 broke almost all our XS modules and nobody cared either (or at
68	root	1.15	least I know of nobody who really complained about gratuitous changes -
69			as opposed to bugs).
70	root	1.11
71			Few modules that are not actively maintained work with newer versions of
72			Perl, regardless of use feature or not, so a new major perl release means
73			changes to many modules - new keywords are just the tip of the iceberg.
74
75	root	1.15	If your code isn't alive, it's dead, Jim - be an active maintainer.
76
77
78	root	1.16	=item no warnings, but a lot of new errors
79	root	1.15
80			Ah, the dreaded warnings. Even worse, the horribly dreaded C<-w>
81			switch: Even though we don't care if other people use warnings (and
82			certainly there are useful ones), a lot of warnings simply go against the
83			spirit of Perl.
84
85			Most prominently, the warnings related to C<undef>. There is nothing wrong
86			with C<undef>: it has well-defined semantics, it is useful, and spitting
87			out warnings you never asked for is just evil.
88
89	root	1.16	The result was that every one of our modules did C<no warnings> in the
90			past, to avoid somebody accidentally using and forcing his bad standards
91			on our code. Of course, this switched off all warnings, even the useful
92			ones. Not a good situation. Really, the C<-w> switch should only enable
93			warnings for the main program only.
94	root	1.15
95			Funnily enough, L<perllexwarn> explicitly mentions C<-w> (and not in a
96			favourable way, calling it outright "wrong"), but standard utilities, such
97			as L<prove>, or MakeMaker when running C<make test>, still enable them
98			blindly.
99
100	root	1.16	For version 2 of common::sense, we finally sat down a few hours and went
101			through I<every single warning message>, identifiying - according to
102			common sense - all the useful ones.
103	root	1.15
104			This resulted in the rather impressive list in the SYNOPSIS. When we
105			weren't sure, we didn't include the warning, so the list might grow in
106			the future (we might have made a mistake, too, so the list might shrink
107	root	1.16	as well).
108	root	1.15
109			Note the presence of C<FATAL> in the list: we do not think that the
110			conditions caught by these warnings are worthy of a warning, we I<insist>
111	root	1.16	that they are worthy of I<stopping> your program, I<instantly>. They are
112			I<bugs>!
113	root	1.15
114			Therefore we consider C<common::sense> to be much stricter than C<use
115			warnings>, which is good if you are into strict things (we are not,
116			actually, but these things tend to be subjective).
117
118			After deciding on the list, we ran the module against all of our code that
119			uses C<common::sense> (that is almost all of our code), and found only one
120			occurence where one of them caused a problem: one of elmex's (unreleased)
121			modules contained:
122
123			$fmt =~ s/([^\s\[])\[( [^\]] )\]/\x0$1\x1$2\x0/xgo;
124
125			We quickly agreed that indeed the code should be changed, even though it
126			happened to do the right thing when the warning was switched off.
127
128	root	1.11
129			=item mucho reduced memory usage
130
131			Just using all those pragmas mentioned in the SYNOPSIS together wastes
132			<blink>I<< B<776> kilobytes >></blink> of precious memory in my perl, for
133			I<every single perl process using our code>, which on our machines, is a
134			lot. In comparison, this module only uses I<< B<four> >> kilobytes (I even
135			had to write it out so it looks like more) of memory on the same platform.
136	root	1.1
137			The money/time/effort/electricity invested in these gigabytes (probably
138			petabytes globally!) of wasted memory could easily save 42 trees, and a
139			kitten!
140
141	root	1.11	Unfortunately, until everybods applies more common sense, there will still
142			often be modules that pull in the monster pragmas. But one can hope...
143
144	root	1.1	=cut
145
146	root	1.2	package common::sense;
147	root	1.1
148	root	1.19	our $VERSION = '2.01';
149	root	1.15
150	root	1.19	# paste this into perl to find bitmask
151	root	1.1
152	root	1.13	# no warnings;
153			# use warnings qw(FATAL closed threads internal debugging pack substr malloc unopened portable prototype
154	root	1.16	# inplace io pipe unpack regexp deprecated exiting glob digit printf
155	root	1.14	# utf8 layer reserved parenthesis taint closure semicolon);
156			# no warnings qw(exec newline);
157			# BEGIN { warn join "", map "\\x$_", unpack "(H2)*", ${^WARNING_BITS}; exit 0 };
158	root	1.13
159			# overload should be included
160
161	root	1.2	sub import {
162	root	1.13	# verified with perl 5.8.0, 5.10.0
163	root	1.19	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\xfc\x3f\xf3\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
164	root	1.3
165			# use strict vars subs
166			$^H \|= 0x00000600;
167
168			# use feature
169			$^H{feature_switch} =
170			$^H{feature_say} =
171			$^H{feature_state} = 1;
172	root	1.1	}
173
174			1;
175
176			=back
177
178	root	1.5	=head1 THERE IS NO 'no common::sense'!!!! !!!! !!
179	root	1.4
180			This module doesn't offer an unimport. First of all, it wastes even more
181			memory, second, and more importantly, who with even a bit of common sense
182			would want no common sense?
183
184	root	1.5	=head1 STABILITY AND FUTURE VERSIONS
185
186			Future versions might change just about everything in this module. We
187			might test our modules and upload new ones working with newer versions of
188			this module, and leave you standing in the rain because we didn't tell
189	root	1.15	you. In fact, we did so when switching from 1.0 to 2.0, which enabled gobs
190			of warnings, and made them FATAL on top.
191	root	1.5
192	root	1.15	Maybe we will load some nifty modules that try to emulate C<say> or so
193			with perls older than 5.10 (this module, of course, should work with older
194			perl versions - supporting 5.8 for example is just common sense at this
195			time. Maybe not in the future, but of course you can trust our common
196			sense to be consistent with, uhm, our opinion).
197	root	1.11
198			=head1 WHAT OTHER PEOPLE HAD TO SAY ABOUT THIS MODULE
199
200			apeiron
201
202			"... wow"
203			"I hope common::sense is a joke."
204
205			crab
206	root	1.5
207	root	1.11	"i wonder how it would be if joerg schilling wrote perl modules."
208	root	1.7
209	root	1.17	Adam Kennedy
210
211			"Very interesting, efficient, and potentially something I'd use all the time."
212			[...]
213			"So no common::sense for me, alas."
214
215	root	1.11	H.Merijn Brand
216
217			"Just one more reason to drop JSON::XS from my distribution list"
218	root	1.7
219			Pista Palo
220
221			"Something in short supply these days..."
222
223			Steffen Schwigon
224
225			"This module is quite for sure not just a repetition of all the other
226			'use strict, use warnings'-approaches, and it's also not the opposite.
227			[...] And for its chosen middle-way it's also not the worst name ever.
228			And everything is documented."
229
230			BKB
231
232			"[Deleted - thanks to Steffen Schwigon for pointing out this review was
233			in error.]"
234
235			Somni
236
237			"the arrogance of the guy"
238			"I swear he tacked somenoe else's name onto the module
239			just so he could use the royal 'we' in the documentation"
240
241			dngor
242
243			"Heh. '"<elmex at ta-sa.org>"' The quotes are semantic
244			distancing from that e-mail address."
245
246			Jerad Pierce
247
248			"Awful name (not a proper pragma), and the SYNOPSIS doesn't tell you
249			anything either. Nor is it clear what features have to do with "common
250			sense" or discipline."
251
252			acme
253
254			"THERE IS NO 'no common::sense'!!!! !!!! !!"
255
256	root	1.15	apeiron (meta-comment about us commenting^Wquoting his comment)
257	root	1.12
258			How about quoting this: get a clue, you fucktarded amoeba.
259
260	root	1.20	quanth
261
262			common sense is beautiful, json::xs is fast, Anyevent, EV are fast and
263			furious. I love mlehmannware ;)
264
265	root	1.19	=head1 FREQUQNTLY ASKED QUESTIONS
266
267			Or frequently-come-up confusions.
268
269			=over 4
270
271			=item Is this module meant to be serious?
272
273			Yes, we would have put it under the C<Acme::> namespace otherwise.
274
275			=item But the manpage is written in a funny/stupid/... way?
276
277			This was meant to make it clear that our common sense is a subjective
278			thing and other people can use their own notions, taking the steam out
279			of anybody who might be offended (as some people are always offended no
280			matter what you do).
281
282			This was a failure.
283
284			But we hope the manpage still is somewhat entertaining even though it
285			explains boring rationale.
286
287			=item Why do you impose your conventions on my code?
288
289			For some reason people keep thinking that C<common::sense> imposes
290			process-wide limits, even though the SYNOPSIS makes it clear that it works
291			like other similar modules - only on the scope that uses them.
292
293			So, no, we don't - nobody is forced to use this module, and using a module
294			that relies on common::sense does not impose anything on you.
295
296			=item Why do you think only your notion of common::sense is valid?
297
298			Well, we don't, and have clearly written this in the documentation to
299			every single release. We were just faster than anybody else w.r.t. to
300			grabbing the namespace.
301
302			=item But everybody knows that you have to use strict and use warnings,
303			why do you disable them?
304
305			Well, we don't do this either - we selectively disagree with the
306			usefulness of some warnings over others. This module is aimed at
307			experienced Perl programmers, not people migrating from other languages
308			who might be surprised about stuff such as C<undef>.
309
310			In fact, this module is considerably I<more> strict than the canonical
311			C<use strict; use warnings>, as it makes all warnings fatal in nature, so
312			you can get away with as many things as with the canonical approach.
313
314			This was not implemented in version 1.0 because of the daunting number
315			of warning categories and the difficulty in getting exactly the set of
316			warnings you wish (i.e. look at the SYNOPSIS in how complicated it is to
317			get a specific set of warnings - it is not reasonable to put this into
318			every module, the maintainance effort would be enourmous).
319
320			=item But many modules C<use strict> or C<use warnings>, so the memory
321			savings do not apply?
322
323			I am suddenly so sad.
324
325			But yes, that's true. Fortunately C<common::sense> still uses only a
326			miniscule amount of RAM.
327
328			=item But it adds another dependency to your modules!
329
330			It's a fact, yeah. But it's trivial to install, most popular modules have
331			many more dependencies and we consider dependencies a good thing - it
332			leads to better APIs, more thought about interworking of modules and so
333			on.
334
335			=item But! But!
336
337			Yeah, we know.
338
339			=back
340
341	root	1.1	=head1 AUTHOR
342
343			Marc Lehmann <schmorp@schmorp.de>
344			http://home.schmorp.de/
345
346	root	1.4	Robin Redeker, "<elmex at ta-sa.org>".
347
348	root	1.1	=cut
349