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.

=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.

=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:	1.19
Committed:	Mon Oct 5 15:02:32 2009 UTC (14 years, 9 months ago) by root
Branch:	MAIN
CVS Tags:	rel-2_01
Changes since 1.18:	+80 -4 lines
Log Message:	2.01
#	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.
25
26	=over 4
27
28	=item use strict qw(subs vars)
29
30	Using C<use strict> is definitely common sense, but C<use strict
31	'refs'> definitely overshoots its usefulness. After almost two
32	decades of Perl hacking, we decided that it does more harm than being
33	useful. Specifically, constructs like these:
34
35	@{ $var->[0] }
36
37	Must be written like this (or similarly), when C<use strict 'refs'> is in
38	scope, and C<$var> can legally be C<undef>:
39
40	@{ $var->[0] \|\| [] }
41
42	This is annoying, and doesn't shield against obvious mistakes such as
43	using C<"">, so one would even have to write (at least for the time
44	being):
45
46	@{ defined $var->[0] ? $var->[0] : [] }
47
48	... which nobody with a bit of common sense would consider
49	writing: clear code is clearly something else.
50
51	Curiously enough, sometimes perl is not so strict, as this works even with
52	C<use strict> in scope:
53
54	for (@{ $var->[0] }) { ...
55
56	If that isn't hypocrisy! And all that from a mere program!
57
58
59	=item use feature qw(say state given)
60
61	We found it annoying that we always have to enable extra features. If
62	something breaks because it didn't anticipate future changes, so be
63	it. 5.10 broke almost all our XS modules and nobody cared either (or at
64	least I know of nobody who really complained about gratuitous changes -
65	as opposed to bugs).
66
67	Few modules that are not actively maintained work with newer versions of
68	Perl, regardless of use feature or not, so a new major perl release means
69	changes to many modules - new keywords are just the tip of the iceberg.
70
71	If your code isn't alive, it's dead, Jim - be an active maintainer.
72
73
74	=item no warnings, but a lot of new errors
75
76	Ah, the dreaded warnings. Even worse, the horribly dreaded C<-w>
77	switch: Even though we don't care if other people use warnings (and
78	certainly there are useful ones), a lot of warnings simply go against the
79	spirit of Perl.
80
81	Most prominently, the warnings related to C<undef>. There is nothing wrong
82	with C<undef>: it has well-defined semantics, it is useful, and spitting
83	out warnings you never asked for is just evil.
84
85	The result was that every one of our modules did C<no warnings> in the
86	past, to avoid somebody accidentally using and forcing his bad standards
87	on our code. Of course, this switched off all warnings, even the useful
88	ones. Not a good situation. Really, the C<-w> switch should only enable
89	warnings for the main program only.
90
91	Funnily enough, L<perllexwarn> explicitly mentions C<-w> (and not in a
92	favourable way, calling it outright "wrong"), but standard utilities, such
93	as L<prove>, or MakeMaker when running C<make test>, still enable them
94	blindly.
95
96	For version 2 of common::sense, we finally sat down a few hours and went
97	through I<every single warning message>, identifiying - according to
98	common sense - all the useful ones.
99
100	This resulted in the rather impressive list in the SYNOPSIS. When we
101	weren't sure, we didn't include the warning, so the list might grow in
102	the future (we might have made a mistake, too, so the list might shrink
103	as well).
104
105	Note the presence of C<FATAL> in the list: we do not think that the
106	conditions caught by these warnings are worthy of a warning, we I<insist>
107	that they are worthy of I<stopping> your program, I<instantly>. They are
108	I<bugs>!
109
110	Therefore we consider C<common::sense> to be much stricter than C<use
111	warnings>, which is good if you are into strict things (we are not,
112	actually, but these things tend to be subjective).
113
114	After deciding on the list, we ran the module against all of our code that
115	uses C<common::sense> (that is almost all of our code), and found only one
116	occurence where one of them caused a problem: one of elmex's (unreleased)
117	modules contained:
118
119	$fmt =~ s/([^\s\[])\[( [^\]] )\]/\x0$1\x1$2\x0/xgo;
120
121	We quickly agreed that indeed the code should be changed, even though it
122	happened to do the right thing when the warning was switched off.
123
124
125	=item mucho reduced memory usage
126
127	Just using all those pragmas mentioned in the SYNOPSIS together wastes
128	<blink>I<< B<776> kilobytes >></blink> of precious memory in my perl, for
129	I<every single perl process using our code>, which on our machines, is a
130	lot. In comparison, this module only uses I<< B<four> >> kilobytes (I even
131	had to write it out so it looks like more) of memory on the same platform.
132
133	The money/time/effort/electricity invested in these gigabytes (probably
134	petabytes globally!) of wasted memory could easily save 42 trees, and a
135	kitten!
136
137	Unfortunately, until everybods applies more common sense, there will still
138	often be modules that pull in the monster pragmas. But one can hope...
139
140	=cut
141
142	package common::sense;
143
144	our $VERSION = '2.01';
145
146	# paste this into perl to find bitmask
147
148	# no warnings;
149	# use warnings qw(FATAL closed threads internal debugging pack substr malloc unopened portable prototype
150	# inplace io pipe unpack regexp deprecated exiting glob digit printf
151	# utf8 layer reserved parenthesis taint closure semicolon);
152	# no warnings qw(exec newline);
153	# BEGIN { warn join "", map "\\x$_", unpack "(H2)*", ${^WARNING_BITS}; exit 0 };
154
155	# overload should be included
156
157	sub import {
158	# verified with perl 5.8.0, 5.10.0
159	${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\xfc\x3f\xf3\x00\x0f\xf3\xcf\xc0\xf3\xfc\x33\x03";
160
161	# use strict vars subs
162	$^H \|= 0x00000600;
163
164	# use feature
165	$^H{feature_switch} =
166	$^H{feature_say} =
167	$^H{feature_state} = 1;
168	}
169
170	1;
171
172	=back
173
174	=head1 THERE IS NO 'no common::sense'!!!! !!!! !!
175
176	This module doesn't offer an unimport. First of all, it wastes even more
177	memory, second, and more importantly, who with even a bit of common sense
178	would want no common sense?
179
180	=head1 STABILITY AND FUTURE VERSIONS
181
182	Future versions might change just about everything in this module. We
183	might test our modules and upload new ones working with newer versions of
184	this module, and leave you standing in the rain because we didn't tell
185	you. In fact, we did so when switching from 1.0 to 2.0, which enabled gobs
186	of warnings, and made them FATAL on top.
187
188	Maybe we will load some nifty modules that try to emulate C<say> or so
189	with perls older than 5.10 (this module, of course, should work with older
190	perl versions - supporting 5.8 for example is just common sense at this
191	time. Maybe not in the future, but of course you can trust our common
192	sense to be consistent with, uhm, our opinion).
193
194	=head1 WHAT OTHER PEOPLE HAD TO SAY ABOUT THIS MODULE
195
196	apeiron
197
198	"... wow"
199	"I hope common::sense is a joke."
200
201	crab
202
203	"i wonder how it would be if joerg schilling wrote perl modules."
204
205	Adam Kennedy
206
207	"Very interesting, efficient, and potentially something I'd use all the time."
208	[...]
209	"So no common::sense for me, alas."
210
211	H.Merijn Brand
212
213	"Just one more reason to drop JSON::XS from my distribution list"
214
215	Pista Palo
216
217	"Something in short supply these days..."
218
219	Steffen Schwigon
220
221	"This module is quite for sure not just a repetition of all the other
222	'use strict, use warnings'-approaches, and it's also not the opposite.
223	[...] And for its chosen middle-way it's also not the worst name ever.
224	And everything is documented."
225
226	BKB
227
228	"[Deleted - thanks to Steffen Schwigon for pointing out this review was
229	in error.]"
230
231	Somni
232
233	"the arrogance of the guy"
234	"I swear he tacked somenoe else's name onto the module
235	just so he could use the royal 'we' in the documentation"
236
237	dngor
238
239	"Heh. '"<elmex at ta-sa.org>"' The quotes are semantic
240	distancing from that e-mail address."
241
242	Jerad Pierce
243
244	"Awful name (not a proper pragma), and the SYNOPSIS doesn't tell you
245	anything either. Nor is it clear what features have to do with "common
246	sense" or discipline."
247
248	acme
249
250	"THERE IS NO 'no common::sense'!!!! !!!! !!"
251
252	apeiron (meta-comment about us commenting^Wquoting his comment)
253
254	How about quoting this: get a clue, you fucktarded amoeba.
255
256	=head1 FREQUQNTLY ASKED QUESTIONS
257
258	Or frequently-come-up confusions.
259
260	=over 4
261
262	=item Is this module meant to be serious?
263
264	Yes, we would have put it under the C<Acme::> namespace otherwise.
265
266	=item But the manpage is written in a funny/stupid/... way?
267
268	This was meant to make it clear that our common sense is a subjective
269	thing and other people can use their own notions, taking the steam out
270	of anybody who might be offended (as some people are always offended no
271	matter what you do).
272
273	This was a failure.
274
275	But we hope the manpage still is somewhat entertaining even though it
276	explains boring rationale.
277
278	=item Why do you impose your conventions on my code?
279
280	For some reason people keep thinking that C<common::sense> imposes
281	process-wide limits, even though the SYNOPSIS makes it clear that it works
282	like other similar modules - only on the scope that uses them.
283
284	So, no, we don't - nobody is forced to use this module, and using a module
285	that relies on common::sense does not impose anything on you.
286
287	=item Why do you think only your notion of common::sense is valid?
288
289	Well, we don't, and have clearly written this in the documentation to
290	every single release. We were just faster than anybody else w.r.t. to
291	grabbing the namespace.
292
293	=item But everybody knows that you have to use strict and use warnings,
294	why do you disable them?
295
296	Well, we don't do this either - we selectively disagree with the
297	usefulness of some warnings over others. This module is aimed at
298	experienced Perl programmers, not people migrating from other languages
299	who might be surprised about stuff such as C<undef>.
300
301	In fact, this module is considerably I<more> strict than the canonical
302	C<use strict; use warnings>, as it makes all warnings fatal in nature, so
303	you can get away with as many things as with the canonical approach.
304
305	This was not implemented in version 1.0 because of the daunting number
306	of warning categories and the difficulty in getting exactly the set of
307	warnings you wish (i.e. look at the SYNOPSIS in how complicated it is to
308	get a specific set of warnings - it is not reasonable to put this into
309	every module, the maintainance effort would be enourmous).
310
311	=item But many modules C<use strict> or C<use warnings>, so the memory
312	savings do not apply?
313
314	I am suddenly so sad.
315
316	But yes, that's true. Fortunately C<common::sense> still uses only a
317	miniscule amount of RAM.
318
319	=item But it adds another dependency to your modules!
320
321	It's a fact, yeah. But it's trivial to install, most popular modules have
322	many more dependencies and we consider dependencies a good thing - it
323	leads to better APIs, more thought about interworking of modules and so
324	on.
325
326	=item But! But!
327
328	Yeah, we know.
329
330	=back
331
332	=head1 AUTHOR
333
334	Marc Lehmann <schmorp@schmorp.de>
335	http://home.schmorp.de/
336
337	Robin Redeker, "<elmex at ta-sa.org>".
338
339	=cut
340