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-=head1 NAME
-
-common::sense - save a tree AND a kitten, use common::sense!
-
-=head1 SYNOPSIS
-
- use common::sense;
-
- # Supposed to be mostly the same, with much lower memory usage, as:
-
- # use utf8;
- # use strict qw(vars subs);
- # use feature qw(say state switch);
- # use feature qw(unicode_strings unicode_eval current_sub fc evalbytes);
- # no feature qw(array_base);
- # no warnings;
- # use warnings qw(FATAL closed threads internal debugging pack
- # portable prototype inplace io pipe unpack malloc
- # glob digit printf layer reserved taint closure
- # semicolon);
- # no warnings qw(exec newline unopened);
-
-=head1 DESCRIPTION
-
- “Nothing is more fairly distributed than common sense: no one thinks
- he needs more of it than he already has.”
-
- – René Descartes
-
-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.
-
-The basic philosophy behind the choices made in common::sense can be
-summarised as: "enforcing strict policies to catch as many bugs as
-possible, while at the same time, not limiting the expressive power
-available to the programmer".
-
-Two typical examples of how this philosophy is applied in practise is the
-handling of uninitialised and malloc warnings:
-
-=over 4
-
-=item I<uninitialised>
-
-C<undef> is a well-defined feature of perl, and enabling warnings for
-using it rarely catches any bugs, but considerably limits you in what you
-can do, so uninitialised warnings are disabled.
-
-=item I<malloc>
-
-Freeing something twice on the C level is a serious bug, usually causing
-memory corruption. It often leads to side effects much later in the
-program and there are no advantages to not reporting this, so malloc
-warnings are fatal by default.
-
-=back
-
-Unfortunately, there is no fine-grained warning control in perl, so often
-whole groups of useful warnings had to be excluded because of a single
-useless warning (for example, perl puts an arbitrary limit on the length
-of text you can match with some regexes before emitting a warning, making
-the whole C<regexp> category useless).
-
-What follows is a more thorough discussion of what this module does,
-and why it does it, and what the advantages (and disadvantages) of this
-approach are.
-
-=head1 RATIONALE
-
-=over 4
-
-=item use utf8
-
-While it's not common sense to write your programs in UTF-8, it's quickly
-becoming the most common encoding, is the designated future default
-encoding for perl sources, and the most convenient encoding available
-(you can do really nice quoting tricks...). Experience has shown that our
-programs were either all pure ascii or utf-8, both of which will stay the
-same.
-
-There are few drawbacks to enabling UTF-8 source code by default (mainly
-some speed hits due to bugs in older versions of perl), so this module
-enables UTF-8 source code encoding by default.
-
-
-=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.
-
-But nobody forces you to use those extra features in modules meant for
-older versions of perl - common::sense of course works there as well.
-There is also an important other mode where having additional features by
-default is useful: commandline hacks and internal use scripts: See "much
-reduced typing", below.
-
-There is one notable exception: C<unicode_eval> is not enabled by
-default. In our opinion, C<use feature> had one main effect - newer perl
-versions don't value backwards compatibility and the ability to write
-modules for multiple perl versions much, after all, you can use feature.
-
-C<unicode_eval> doesn't add a new feature, it breaks an existing function.
-
-=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>, identifying - 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
-occurrence 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 much reduced typing
-
-Especially with version 2.0 of common::sense, the amount of boilerplate
-code you need to add to get I<this> policy is daunting. Nobody would write
-this out in throwaway scripts, commandline hacks or in quick internal-use
-scripts.
-
-By using common::sense you get a defined set of policies (ours, but maybe
-yours, too, if you accept them), and they are easy to apply to your
-scripts: typing C<use common::sense;> is even shorter than C<use warnings;
-use strict; use feature ...>.
-
-And you can immediately use the features of your installed perl, which
-is more difficult in code you release, but not usually an issue for
-internal-use code (downgrades of your production perl should be rare,
-right?).
-
-
-=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 everybody applies more common sense, there will still
-often be modules that pull in the monster pragmas. But one can hope...
-
-=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"
-
-Anonymous Monk
-
- "You just gotta love this thing, its got META.json!!!"
-
-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 ;)"
-
-apeiron
-
- "... it's mlehmann's view of what common sense is. His view of common
- sense is certainly uncommon, insofar as anyone with a clue disagrees
- with him."
-
-apeiron (another meta-comment)
-
- "apeiron wonders if his little informant is here to steal more quotes"
-
-ew73
-
- "... I never got past the SYNOPSIS before calling it shit."
- [...]
- How come no one ever quotes me. :("
-
-chip (not willing to explain his cryptic questions about links in Changes files)
-
- "I'm willing to ask the question I've asked. I'm not willing to go
- through the whole dance you apparently have choreographed. Either
- answer the completely obvious question, or tell me to fuck off again."
-
-=head1 FREQUENTLY 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 - i.e. only within the scope that C<use>s 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>. On the other hand,
-this does not exclude the usefulness of this module for total newbies, due
-to its strictness in enforcing policy, while at the same time not limiting
-the expressive power of perl.
-
-This module is considerably I<more> strict than the canonical C<use
-strict; use warnings>, as it makes all its warnings fatal in nature, so
-you can not 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 maintenance effort would be enormous).
-
-=item But many modules C<use strict> or C<use warnings>, so the memory
-savings do not apply?
-
-I suddenly feel 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 Why do you use JSON and not YAML for your META.yml?
-
-This is not true - YAML supports a large subset of JSON, and this subset
-is what META.yml is written in, so it would be correct to say "the
-META.yml is written in a common subset of YAML and JSON".
-
-The META.yml follows the YAML, JSON and META.yml specifications, and is
-correctly parsed by CPAN, so if you have trouble with it, the problem is
-likely on your side.
-
-=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
-