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 *
#	Content
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	# supposed to be the same, with much lower memory usage, as:
10	#
11	# use strict qw(vars subs);
12	# use feature qw(say state switch);
13	# no warnings;
14	# use warnings qw(FATAL closed threads internal debugging pack substr malloc
15	# unopened portable prototype inplace io pipe unpack regexp
16	# deprecated exiting glob digit printf utf8 layer
17	# reserved parenthesis taint closure semicolon);
18	# no warnings qw(exec newline);
19
20	=head1 DESCRIPTION
21
22	This module implements some sane defaults for Perl programs, as defined by
23	two typical (or not so typical - use your common sense) specimens of Perl
24	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
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	'refs'> definitely overshoots its usefulness. After almost two
36	decades of Perl hacking, we decided that it does more harm than being
37	useful. Specifically, constructs like these:
38
39	@{ $var->[0] }
40
41	Must be written like this (or similarly), when C<use strict 'refs'> is in
42	scope, and C<$var> can legally be C<undef>:
43
44	@{ $var->[0] \|\| [] }
45
46	This is annoying, and doesn't shield against obvious mistakes such as
47	using C<"">, so one would even have to write (at least for the time
48	being):
49
50	@{ defined $var->[0] ? $var->[0] : [] }
51
52	... which nobody with a bit of common sense would consider
53	writing: clear code is clearly something else.
54
55	Curiously enough, sometimes perl is not so strict, as this works even with
56	C<use strict> in scope:
57
58	for (@{ $var->[0] }) { ...
59
60	If that isn't hypocrisy! And all that from a mere program!
61
62
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	it. 5.10 broke almost all our XS modules and nobody cared either (or at
68	least I know of nobody who really complained about gratuitous changes -
69	as opposed to bugs).
70
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	If your code isn't alive, it's dead, Jim - be an active maintainer.
76
77
78	=item no warnings, but a lot of new errors
79
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	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
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	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
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	as well).
108
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	that they are worthy of I<stopping> your program, I<instantly>. They are
112	I<bugs>!
113
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
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
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	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	=cut
145
146	package common::sense;
147
148	our $VERSION = '2.01';
149
150	# paste this into perl to find bitmask
151
152	# no warnings;
153	# use warnings qw(FATAL closed threads internal debugging pack substr malloc unopened portable prototype
154	# inplace io pipe unpack regexp deprecated exiting glob digit printf
155	# utf8 layer reserved parenthesis taint closure semicolon);
156	# no warnings qw(exec newline);
157	# BEGIN { warn join "", map "\\x$_", unpack "(H2)*", ${^WARNING_BITS}; exit 0 };
158
159	# overload should be included
160
161	sub import {
162	# verified with perl 5.8.0, 5.10.0
163	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\xfc\x3f\xf3\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
164
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	}
173
174	1;
175
176	=back
177
178	=head1 THERE IS NO 'no common::sense'!!!! !!!! !!
179
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	=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	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
192	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
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
207	"i wonder how it would be if joerg schilling wrote perl modules."
208
209	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	H.Merijn Brand
216
217	"Just one more reason to drop JSON::XS from my distribution list"
218
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	apeiron (meta-comment about us commenting^Wquoting his comment)
257
258	How about quoting this: get a clue, you fucktarded amoeba.
259
260	quanth
261
262	common sense is beautiful, json::xs is fast, Anyevent, EV are fast and
263	furious. I love mlehmannware ;)
264
265	=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	=head1 AUTHOR
342
343	Marc Lehmann <schmorp@schmorp.de>
344	http://home.schmorp.de/
345
346	Robin Redeker, "<elmex at ta-sa.org>".
347
348	=cut
349