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1 | |||||
2 | =head1 NAME | ||||
3 | |||||
4 | common::sense - save a tree AND a kitten, use common::sense! | ||||
5 | |||||
6 | =head1 SYNOPSIS | ||||
7 | |||||
8 | use common::sense; | ||||
9 | |||||
10 | # supposed to be the same, with much lower memory usage, as: | ||||
11 | # | ||||
12 | # use utf8; | ||||
13 | # use strict qw(vars subs); | ||||
14 | # use feature qw(say state switch); | ||||
15 | # no warnings; | ||||
16 | # use warnings qw(FATAL closed threads internal debugging pack | ||||
17 | # portable prototype inplace io pipe unpack malloc | ||||
18 | # deprecated glob digit printf layer | ||||
19 | # reserved taint closure semicolon); | ||||
20 | # no warnings qw(exec newline unopened); | ||||
21 | |||||
22 | |||||
23 | =head1 DESCRIPTION | ||||
24 | |||||
25 | “Nothing is more fairly distributed than common sense: no one thinks | ||||
26 | he needs more of it than he already has.” | ||||
27 | |||||
28 | – René Descartes | ||||
29 | |||||
30 | This module implements some sane defaults for Perl programs, as defined by | ||||
31 | two typical (or not so typical - use your common sense) specimens of Perl | ||||
32 | coders. In fact, after working out details on which warnings and strict | ||||
33 | modes to enable and make fatal, we found that we (and our code written so | ||||
34 | far, and others) fully agree on every option, even though we never used | ||||
35 | warnings before, so it seems this module indeed reflects a "common" sense | ||||
36 | among some long-time Perl coders. | ||||
37 | |||||
38 | The basic philosophy behind the choices made in common::sense can be | ||||
39 | summarised as: "enforcing strict policies to catch as many bugs as | ||||
40 | possible, while at the same time, not limiting the expressive power | ||||
41 | available to the programmer". | ||||
42 | |||||
43 | Two typical examples of how this philosophy is applied in practise is the | ||||
44 | handling of uninitialised and malloc warnings: | ||||
45 | |||||
46 | =over 4 | ||||
47 | |||||
48 | =item I<uninitialised> | ||||
49 | |||||
50 | C<undef> is a well-defined feature of perl, and enabling warnings for | ||||
51 | using it rarely catches any bugs, but considerably limits you in what you | ||||
52 | can do, so uninitialised warnings are disabled. | ||||
53 | |||||
54 | =item I<malloc> | ||||
55 | |||||
56 | Freeing something twice on the C level is a serious bug, usually causing | ||||
57 | memory corruption. It often leads to side effects much later in the | ||||
58 | program and there are no advantages to not reporting this, so malloc | ||||
59 | warnings are fatal by default. | ||||
60 | |||||
61 | =back | ||||
62 | |||||
63 | Unfortunately, there is no fine-grained warning control in perl, so often | ||||
64 | whole groups of useful warnings had to be excluded because of a single | ||||
65 | useless warning (for example, perl puts an arbitrary limit on the length | ||||
66 | of text you can match with some regexes before emitting a warning, making | ||||
67 | the whole C<regexp> category useless). | ||||
68 | |||||
69 | What follows is a more thorough discussion of what this module does, | ||||
70 | and why it does it, and what the advantages (and disadvantages) of this | ||||
71 | approach are. | ||||
72 | |||||
73 | =head1 RATIONALE | ||||
74 | |||||
75 | =over 4 | ||||
76 | |||||
77 | =item use utf8 | ||||
78 | |||||
79 | While it's not common sense to write your programs in UTF-8, it's quickly | ||||
80 | becoming the most common encoding, is the designated future default | ||||
81 | encoding for perl sources, and the most convenient encoding available | ||||
82 | (you can do really nice quoting tricks...). Experience has shown that our | ||||
83 | programs were either all pure ascii or utf-8, both of which will stay the | ||||
84 | same. | ||||
85 | |||||
86 | There are few drawbacks to enabling UTF-8 source code by default (mainly | ||||
87 | some speed hits due to bugs in older versions of perl), so this module | ||||
88 | enables UTF-8 source code encoding by default. | ||||
89 | |||||
90 | |||||
91 | =item use strict qw(subs vars) | ||||
92 | |||||
93 | Using C<use strict> is definitely common sense, but C<use strict | ||||
94 | 'refs'> definitely overshoots its usefulness. After almost two | ||||
95 | decades of Perl hacking, we decided that it does more harm than being | ||||
96 | useful. Specifically, constructs like these: | ||||
97 | |||||
98 | @{ $var->[0] } | ||||
99 | |||||
100 | Must be written like this (or similarly), when C<use strict 'refs'> is in | ||||
101 | scope, and C<$var> can legally be C<undef>: | ||||
102 | |||||
103 | @{ $var->[0] || [] } | ||||
104 | |||||
105 | This is annoying, and doesn't shield against obvious mistakes such as | ||||
106 | using C<"">, so one would even have to write (at least for the time | ||||
107 | being): | ||||
108 | |||||
109 | @{ defined $var->[0] ? $var->[0] : [] } | ||||
110 | |||||
111 | ... which nobody with a bit of common sense would consider | ||||
112 | writing: clear code is clearly something else. | ||||
113 | |||||
114 | Curiously enough, sometimes perl is not so strict, as this works even with | ||||
115 | C<use strict> in scope: | ||||
116 | |||||
117 | for (@{ $var->[0] }) { ... | ||||
118 | |||||
119 | If that isn't hypocrisy! And all that from a mere program! | ||||
120 | |||||
121 | |||||
122 | =item use feature qw(say state given) | ||||
123 | |||||
124 | We found it annoying that we always have to enable extra features. If | ||||
125 | something breaks because it didn't anticipate future changes, so be | ||||
126 | it. 5.10 broke almost all our XS modules and nobody cared either (or at | ||||
127 | least I know of nobody who really complained about gratuitous changes - | ||||
128 | as opposed to bugs). | ||||
129 | |||||
130 | Few modules that are not actively maintained work with newer versions of | ||||
131 | Perl, regardless of use feature or not, so a new major perl release means | ||||
132 | changes to many modules - new keywords are just the tip of the iceberg. | ||||
133 | |||||
134 | If your code isn't alive, it's dead, Jim - be an active maintainer. | ||||
135 | |||||
136 | But nobody forces you to use those extra features in modules meant for | ||||
137 | older versions of perl - common::sense of course works there as well. | ||||
138 | There is also an important other mode where having additional features by | ||||
139 | default is useful: commandline hacks and internal use scripts: See "much | ||||
140 | reduced typing", below. | ||||
141 | |||||
142 | |||||
143 | =item no warnings, but a lot of new errors | ||||
144 | |||||
145 | Ah, the dreaded warnings. Even worse, the horribly dreaded C<-w> | ||||
146 | switch: Even though we don't care if other people use warnings (and | ||||
147 | certainly there are useful ones), a lot of warnings simply go against the | ||||
148 | spirit of Perl. | ||||
149 | |||||
150 | Most prominently, the warnings related to C<undef>. There is nothing wrong | ||||
151 | with C<undef>: it has well-defined semantics, it is useful, and spitting | ||||
152 | out warnings you never asked for is just evil. | ||||
153 | |||||
154 | The result was that every one of our modules did C<no warnings> in the | ||||
155 | past, to avoid somebody accidentally using and forcing his bad standards | ||||
156 | on our code. Of course, this switched off all warnings, even the useful | ||||
157 | ones. Not a good situation. Really, the C<-w> switch should only enable | ||||
158 | warnings for the main program only. | ||||
159 | |||||
160 | Funnily enough, L<perllexwarn> explicitly mentions C<-w> (and not in a | ||||
161 | favourable way, calling it outright "wrong"), but standard utilities, such | ||||
162 | as L<prove>, or MakeMaker when running C<make test>, still enable them | ||||
163 | blindly. | ||||
164 | |||||
165 | For version 2 of common::sense, we finally sat down a few hours and went | ||||
166 | through I<every single warning message>, identifiying - according to | ||||
167 | common sense - all the useful ones. | ||||
168 | |||||
169 | This resulted in the rather impressive list in the SYNOPSIS. When we | ||||
170 | weren't sure, we didn't include the warning, so the list might grow in | ||||
171 | the future (we might have made a mistake, too, so the list might shrink | ||||
172 | as well). | ||||
173 | |||||
174 | Note the presence of C<FATAL> in the list: we do not think that the | ||||
175 | conditions caught by these warnings are worthy of a warning, we I<insist> | ||||
176 | that they are worthy of I<stopping> your program, I<instantly>. They are | ||||
177 | I<bugs>! | ||||
178 | |||||
179 | Therefore we consider C<common::sense> to be much stricter than C<use | ||||
180 | warnings>, which is good if you are into strict things (we are not, | ||||
181 | actually, but these things tend to be subjective). | ||||
182 | |||||
183 | After deciding on the list, we ran the module against all of our code that | ||||
184 | uses C<common::sense> (that is almost all of our code), and found only one | ||||
185 | occurence where one of them caused a problem: one of elmex's (unreleased) | ||||
186 | modules contained: | ||||
187 | |||||
188 | $fmt =~ s/([^\s\[]*)\[( [^\]]* )\]/\x0$1\x1$2\x0/xgo; | ||||
189 | |||||
190 | We quickly agreed that indeed the code should be changed, even though it | ||||
191 | happened to do the right thing when the warning was switched off. | ||||
192 | |||||
193 | |||||
194 | =item much reduced typing | ||||
195 | |||||
196 | Especially with version 2.0 of common::sense, the amount of boilerplate | ||||
197 | code you need to add to gte I<this> policy is daunting. Nobody would write | ||||
198 | this out in throwaway scripts, commandline hacks or in quick internal-use | ||||
199 | scripts. | ||||
200 | |||||
201 | By using common::sense you get a defined set of policies (ours, but maybe | ||||
202 | yours, too, if you accept them), and they are easy to apply to your | ||||
203 | scripts: typing C<use common::sense;> is even shorter than C<use warnings; | ||||
204 | use strict; use feature ...>. | ||||
205 | |||||
206 | And you can immediately use the features of your installed perl, which | ||||
207 | is more difficult in code you release, but not usually an issue for | ||||
208 | internal-use code (downgrades of your production perl should be rare, | ||||
209 | right?). | ||||
210 | |||||
211 | |||||
212 | =item mucho reduced memory usage | ||||
213 | |||||
214 | Just using all those pragmas mentioned in the SYNOPSIS together wastes | ||||
215 | <blink>I<< B<776> kilobytes >></blink> of precious memory in my perl, for | ||||
216 | I<every single perl process using our code>, which on our machines, is a | ||||
217 | lot. In comparison, this module only uses I<< B<four> >> kilobytes (I even | ||||
218 | had to write it out so it looks like more) of memory on the same platform. | ||||
219 | |||||
220 | The money/time/effort/electricity invested in these gigabytes (probably | ||||
221 | petabytes globally!) of wasted memory could easily save 42 trees, and a | ||||
222 | kitten! | ||||
223 | |||||
224 | Unfortunately, until everybods applies more common sense, there will still | ||||
225 | often be modules that pull in the monster pragmas. But one can hope... | ||||
226 | |||||
227 | =cut | ||||
228 | |||||
229 | package common::sense; | ||||
230 | |||||
231 | 1 | 3µs | our $VERSION = '3.5'; | ||
232 | |||||
233 | # overload should be included | ||||
234 | |||||
235 | # spent 60µs within common::sense::import which was called:
# once (60µs+0s) by JSON::XS::BEGIN@104 at line 104 of JSON/XS.pm | ||||
236 | 4 | 94µs | local $^W; # work around perl 5.16 spewing out warnings for next line | ||
237 | # use warnings | ||||
238 | ${^WARNING_BITS} ^= ${^WARNING_BITS} ^ "\x3c\x3f\x33\x00\x0f\xf0\x0f\xc0\xf0\xfc\x33\x00\x00"; | ||||
239 | # use strict, use utf8; | ||||
240 | $^H |= 0x800600; | ||||
241 | # use feature | ||||
242 | $^H{feature_switch} = | ||||
243 | $^H{feature_say} = | ||||
244 | $^H{feature_state} = 1; | ||||
245 | } | ||||
246 | |||||
247 | 1 | 14µs | 1; | ||
248 | |||||
249 | =back | ||||
250 | |||||
251 | =head1 THERE IS NO 'no common::sense'!!!! !!!! !! | ||||
252 | |||||
253 | This module doesn't offer an unimport. First of all, it wastes even more | ||||
254 | memory, second, and more importantly, who with even a bit of common sense | ||||
255 | would want no common sense? | ||||
256 | |||||
257 | =head1 STABILITY AND FUTURE VERSIONS | ||||
258 | |||||
259 | Future versions might change just about everything in this module. We | ||||
260 | might test our modules and upload new ones working with newer versions of | ||||
261 | this module, and leave you standing in the rain because we didn't tell | ||||
262 | you. In fact, we did so when switching from 1.0 to 2.0, which enabled gobs | ||||
263 | of warnings, and made them FATAL on top. | ||||
264 | |||||
265 | Maybe we will load some nifty modules that try to emulate C<say> or so | ||||
266 | with perls older than 5.10 (this module, of course, should work with older | ||||
267 | perl versions - supporting 5.8 for example is just common sense at this | ||||
268 | time. Maybe not in the future, but of course you can trust our common | ||||
269 | sense to be consistent with, uhm, our opinion). | ||||
270 | |||||
271 | =head1 WHAT OTHER PEOPLE HAD TO SAY ABOUT THIS MODULE | ||||
272 | |||||
273 | apeiron | ||||
274 | |||||
275 | "... wow" | ||||
276 | "I hope common::sense is a joke." | ||||
277 | |||||
278 | crab | ||||
279 | |||||
280 | "i wonder how it would be if joerg schilling wrote perl modules." | ||||
281 | |||||
282 | Adam Kennedy | ||||
283 | |||||
284 | "Very interesting, efficient, and potentially something I'd use all the time." | ||||
285 | [...] | ||||
286 | "So no common::sense for me, alas." | ||||
287 | |||||
288 | H.Merijn Brand | ||||
289 | |||||
290 | "Just one more reason to drop JSON::XS from my distribution list" | ||||
291 | |||||
292 | Pista Palo | ||||
293 | |||||
294 | "Something in short supply these days..." | ||||
295 | |||||
296 | Steffen Schwigon | ||||
297 | |||||
298 | "This module is quite for sure *not* just a repetition of all the other | ||||
299 | 'use strict, use warnings'-approaches, and it's also not the opposite. | ||||
300 | [...] And for its chosen middle-way it's also not the worst name ever. | ||||
301 | And everything is documented." | ||||
302 | |||||
303 | BKB | ||||
304 | |||||
305 | "[Deleted - thanks to Steffen Schwigon for pointing out this review was | ||||
306 | in error.]" | ||||
307 | |||||
308 | Somni | ||||
309 | |||||
310 | "the arrogance of the guy" | ||||
311 | "I swear he tacked somenoe else's name onto the module | ||||
312 | just so he could use the royal 'we' in the documentation" | ||||
313 | |||||
314 | Anonymous Monk | ||||
315 | |||||
316 | "You just gotta love this thing, its got META.json!!!" | ||||
317 | |||||
318 | dngor | ||||
319 | |||||
320 | "Heh. '"<elmex at ta-sa.org>"' The quotes are semantic | ||||
321 | distancing from that e-mail address." | ||||
322 | |||||
323 | Jerad Pierce | ||||
324 | |||||
325 | "Awful name (not a proper pragma), and the SYNOPSIS doesn't tell you | ||||
326 | anything either. Nor is it clear what features have to do with "common | ||||
327 | sense" or discipline." | ||||
328 | |||||
329 | acme | ||||
330 | |||||
331 | "THERE IS NO 'no common::sense'!!!! !!!! !!" | ||||
332 | |||||
333 | apeiron (meta-comment about us commenting^Wquoting his comment) | ||||
334 | |||||
335 | "How about quoting this: get a clue, you fucktarded amoeba." | ||||
336 | |||||
337 | quanth | ||||
338 | |||||
339 | "common sense is beautiful, json::xs is fast, Anyevent, EV are fast and | ||||
340 | furious. I love mlehmannware ;)" | ||||
341 | |||||
342 | apeiron | ||||
343 | |||||
344 | "... it's mlehmann's view of what common sense is. His view of common | ||||
345 | sense is certainly uncommon, insofar as anyone with a clue disagrees | ||||
346 | with him." | ||||
347 | |||||
348 | apeiron (another meta-comment) | ||||
349 | |||||
350 | "apeiron wonders if his little informant is here to steal more quotes" | ||||
351 | |||||
352 | ew73 | ||||
353 | |||||
354 | "... I never got past the SYNOPSIS before calling it shit." | ||||
355 | [...] | ||||
356 | How come no one ever quotes me. :(" | ||||
357 | |||||
358 | chip (not willing to explain his cryptic questions about links in Changes files) | ||||
359 | |||||
360 | "I'm willing to ask the question I've asked. I'm not willing to go | ||||
361 | through the whole dance you apparently have choreographed. Either | ||||
362 | answer the completely obvious question, or tell me to fuck off again." | ||||
363 | |||||
364 | =head1 FREQUENTLY ASKED QUESTIONS | ||||
365 | |||||
366 | Or frequently-come-up confusions. | ||||
367 | |||||
368 | =over 4 | ||||
369 | |||||
370 | =item Is this module meant to be serious? | ||||
371 | |||||
372 | Yes, we would have put it under the C<Acme::> namespace otherwise. | ||||
373 | |||||
374 | =item But the manpage is written in a funny/stupid/... way? | ||||
375 | |||||
376 | This was meant to make it clear that our common sense is a subjective | ||||
377 | thing and other people can use their own notions, taking the steam out | ||||
378 | of anybody who might be offended (as some people are always offended no | ||||
379 | matter what you do). | ||||
380 | |||||
381 | This was a failure. | ||||
382 | |||||
383 | But we hope the manpage still is somewhat entertaining even though it | ||||
384 | explains boring rationale. | ||||
385 | |||||
386 | =item Why do you impose your conventions on my code? | ||||
387 | |||||
388 | For some reason people keep thinking that C<common::sense> imposes | ||||
389 | process-wide limits, even though the SYNOPSIS makes it clear that it works | ||||
390 | like other similar modules - i.e. only within the scope that C<use>s them. | ||||
391 | |||||
392 | So, no, we don't - nobody is forced to use this module, and using a module | ||||
393 | that relies on common::sense does not impose anything on you. | ||||
394 | |||||
395 | =item Why do you think only your notion of common::sense is valid? | ||||
396 | |||||
397 | Well, we don't, and have clearly written this in the documentation to | ||||
398 | every single release. We were just faster than anybody else w.r.t. to | ||||
399 | grabbing the namespace. | ||||
400 | |||||
401 | =item But everybody knows that you have to use strict and use warnings, | ||||
402 | why do you disable them? | ||||
403 | |||||
404 | Well, we don't do this either - we selectively disagree with the | ||||
405 | usefulness of some warnings over others. This module is aimed at | ||||
406 | experienced Perl programmers, not people migrating from other languages | ||||
407 | who might be surprised about stuff such as C<undef>. On the other hand, | ||||
408 | this does not exclude the usefulness of this module for total newbies, due | ||||
409 | to its strictness in enforcing policy, while at the same time not limiting | ||||
410 | the expressive power of perl. | ||||
411 | |||||
412 | This module is considerably I<more> strict than the canonical C<use | ||||
413 | strict; use warnings>, as it makes all its warnings fatal in nature, so | ||||
414 | you can not get away with as many things as with the canonical approach. | ||||
415 | |||||
416 | This was not implemented in version 1.0 because of the daunting number | ||||
417 | of warning categories and the difficulty in getting exactly the set of | ||||
418 | warnings you wish (i.e. look at the SYNOPSIS in how complicated it is to | ||||
419 | get a specific set of warnings - it is not reasonable to put this into | ||||
420 | every module, the maintenance effort would be enourmous). | ||||
421 | |||||
422 | =item But many modules C<use strict> or C<use warnings>, so the memory | ||||
423 | savings do not apply? | ||||
424 | |||||
425 | I suddenly feel sad... | ||||
426 | |||||
427 | But yes, that's true. Fortunately C<common::sense> still uses only a | ||||
428 | miniscule amount of RAM. | ||||
429 | |||||
430 | =item But it adds another dependency to your modules! | ||||
431 | |||||
432 | It's a fact, yeah. But it's trivial to install, most popular modules have | ||||
433 | many more dependencies and we consider dependencies a good thing - it | ||||
434 | leads to better APIs, more thought about interworking of modules and so | ||||
435 | on. | ||||
436 | |||||
437 | =item Why do you use JSON and not YAML for your META.yml? | ||||
438 | |||||
439 | This is not true - YAML supports a large subset of JSON, and this subset | ||||
440 | is what META.yml is written in, so it would be correct to say "the | ||||
441 | META.yml is written in a common subset of YAML and JSON". | ||||
442 | |||||
443 | The META.yml follows the YAML, JSON and META.yml specifications, and is | ||||
444 | correctly parsed by CPAN, so if you have trouble with it, the problem is | ||||
445 | likely on your side. | ||||
446 | |||||
447 | =item But! But! | ||||
448 | |||||
449 | Yeah, we know. | ||||
450 | |||||
451 | =back | ||||
452 | |||||
453 | =head1 AUTHOR | ||||
454 | |||||
455 | Marc Lehmann <schmorp@schmorp.de> | ||||
456 | http://home.schmorp.de/ | ||||
457 | |||||
458 | Robin Redeker, "<elmex at ta-sa.org>". | ||||
459 | |||||
460 | =cut | ||||
461 |