ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/common-sense/sense.pod
Revision: 1.3
Committed: Thu Apr 2 07:53:41 2020 UTC (4 years, 3 months ago) by root
Branch: MAIN
CVS Tags: rel-3_75, HEAD
Changes since 1.2: +2 -3 lines
Log Message:
3.75

File Contents

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