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=head1 NAME |
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|
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common::sense - save a tree AND a kitten, use common::sense! |
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|
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=head1 SYNOPSIS |
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|
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use common::sense; |
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|
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# Supposed to be mostly the same, with much lower memory usage, as: |
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|
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# use utf8; |
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# use strict qw(vars subs); |
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# use feature qw(say state switch); |
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# use feature qw(unicode_strings unicode_eval current_sub fc evalbytes); |
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# no feature qw(array_base); |
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# no warnings; |
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# use warnings qw(FATAL closed threads internal debugging pack |
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# prototype inplace io pipe unpack malloc glob |
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# digit printf layer reserved taint closure semicolon); |
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# no warnings qw(exec newline unopened); |
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|
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=head1 DESCRIPTION |
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|
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“Nothing is more fairly distributed than common sense: no one thinks |
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he needs more of it than he already has.” |
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|
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– René Descartes |
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|
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This module implements some sane defaults for Perl programs, as defined by |
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two typical (or not so typical - use your common sense) specimens of Perl |
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coders. In fact, after working out details on which warnings and strict |
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modes to enable and make fatal, we found that we (and our code written so |
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far, and others) fully agree on every option, even though we never used |
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warnings before, so it seems this module indeed reflects a "common" sense |
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among some long-time Perl coders. |
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|
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The basic philosophy behind the choices made in common::sense can be |
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summarised as: "enforcing strict policies to catch as many bugs as |
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possible, while at the same time, not limiting the expressive power |
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available to the programmer". |
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|
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Two typical examples of how this philosophy is applied in practise is the |
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handling of uninitialised and malloc warnings: |
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|
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=over 4 |
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|
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=item I<uninitialised> |
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|
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C<undef> is a well-defined feature of perl, and enabling warnings for |
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using it rarely catches any bugs, but considerably limits you in what you |
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can do, so uninitialised warnings are disabled. |
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|
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=item I<malloc> |
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|
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Freeing something twice on the C level is a serious bug, usually causing |
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memory corruption. It often leads to side effects much later in the |
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program and there are no advantages to not reporting this, so malloc |
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warnings are fatal by default. |
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|
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=back |
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|
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Unfortunately, there is no fine-grained warning control in perl, so often |
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whole groups of useful warnings had to be excluded because of a single |
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useless warning (for example, perl puts an arbitrary limit on the length |
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of text you can match with some regexes before emitting a warning, making |
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the whole C<regexp> category useless). |
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|
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What follows is a more thorough discussion of what this module does, |
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and why it does it, and what the advantages (and disadvantages) of this |
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approach are. |
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|
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=head1 RATIONALE |
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|
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=over 4 |
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|
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=item use utf8 |
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|
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While it's not common sense to write your programs in UTF-8, it's quickly |
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becoming the most common encoding, is the designated future default |
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encoding for perl sources, and the most convenient encoding available |
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(you can do really nice quoting tricks...). Experience has shown that our |
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programs were either all pure ascii or utf-8, both of which will stay the |
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same. |
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|
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There are few drawbacks to enabling UTF-8 source code by default (mainly |
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some speed hits due to bugs in older versions of perl), so this module |
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enables UTF-8 source code encoding by default. |
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|
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|
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=item use strict qw(subs vars) |
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|
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Using C<use strict> is definitely common sense, but C<use strict |
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'refs'> definitely overshoots its usefulness. After almost two |
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decades of Perl hacking, we decided that it does more harm than being |
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useful. Specifically, constructs like these: |
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|
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@{ $var->[0] } |
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|
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Must be written like this (or similarly), when C<use strict 'refs'> is in |
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scope, and C<$var> can legally be C<undef>: |
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|
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@{ $var->[0] || [] } |
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|
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This is annoying, and doesn't shield against obvious mistakes such as |
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using C<"">, so one would even have to write (at least for the time |
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being): |
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|
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@{ defined $var->[0] ? $var->[0] : [] } |
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|
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... which nobody with a bit of common sense would consider |
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writing: clear code is clearly something else. |
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|
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Curiously enough, sometimes perl is not so strict, as this works even with |
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C<use strict> in scope: |
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|
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for (@{ $var->[0] }) { ... |
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|
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If that isn't hypocrisy! And all that from a mere program! |
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|
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|
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=item use feature qw(say state given ...) |
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|
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We found it annoying that we always have to enable extra features. If |
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something breaks because it didn't anticipate future changes, so be |
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it. 5.10 broke almost all our XS modules and nobody cared either (or at |
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least I know of nobody who really complained about gratuitous changes - |
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as opposed to bugs). |
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|
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Few modules that are not actively maintained work with newer versions of |
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Perl, regardless of use feature or not, so a new major perl release means |
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changes to many modules - new keywords are just the tip of the iceberg. |
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|
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If your code isn't alive, it's dead, Jim - be an active maintainer. |
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|
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But nobody forces you to use those extra features in modules meant for |
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older versions of perl - common::sense of course works there as well. |
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There is also an important other mode where having additional features by |
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default is useful: commandline hacks and internal use scripts: See "much |
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reduced typing", below. |
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|
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There is one notable exception: C<unicode_eval> is not enabled by |
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default. In our opinion, C<use feature> had one main effect - newer perl |
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versions don't value backwards compatibility and the ability to write |
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modules for multiple perl versions much, after all, you can use feature. |
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|
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C<unicode_eval> doesn't add a new feature, it breaks an existing function. |
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|
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=item no warnings, but a lot of new errors |
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|
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Ah, the dreaded warnings. Even worse, the horribly dreaded C<-w> |
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switch: Even though we don't care if other people use warnings (and |
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certainly there are useful ones), a lot of warnings simply go against the |
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spirit of Perl. |
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|
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Most prominently, the warnings related to C<undef>. There is nothing wrong |
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with C<undef>: it has well-defined semantics, it is useful, and spitting |
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out warnings you never asked for is just evil. |
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|
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The result was that every one of our modules did C<no warnings> in the |
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past, to avoid somebody accidentally using and forcing his bad standards |
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on our code. Of course, this switched off all warnings, even the useful |
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ones. Not a good situation. Really, the C<-w> switch should only enable |
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warnings for the main program only. |
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|
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Funnily enough, L<perllexwarn> explicitly mentions C<-w> (and not in a |
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favourable way, calling it outright "wrong"), but standard utilities, such |
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as L<prove>, or MakeMaker when running C<make test>, still enable them |
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blindly. |
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|
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For version 2 of common::sense, we finally sat down a few hours and went |
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through I<every single warning message>, identifying - according to |
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common sense - all the useful ones. |
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|
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This resulted in the rather impressive list in the SYNOPSIS. When we |
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weren't sure, we didn't include the warning, so the list might grow in |
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the future (we might have made a mistake, too, so the list might shrink |
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as well). |
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|
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Note the presence of C<FATAL> in the list: we do not think that the |
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conditions caught by these warnings are worthy of a warning, we I<insist> |
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that they are worthy of I<stopping> your program, I<instantly>. They are |
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I<bugs>! |
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|
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Therefore we consider C<common::sense> to be much stricter than C<use |
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warnings>, which is good if you are into strict things (we are not, |
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actually, but these things tend to be subjective). |
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|
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After deciding on the list, we ran the module against all of our code that |
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uses C<common::sense> (that is almost all of our code), and found only one |
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occurrence where one of them caused a problem: one of elmex's (unreleased) |
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modules contained: |
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|
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$fmt =~ s/([^\s\[]*)\[( [^\]]* )\]/\x0$1\x1$2\x0/xgo; |
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|
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We quickly agreed that indeed the code should be changed, even though it |
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happened to do the right thing when the warning was switched off. |
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|
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|
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=item much reduced typing |
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|
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Especially with version 2.0 of common::sense, the amount of boilerplate |
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code you need to add to get I<this> policy is daunting. Nobody would write |
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this out in throwaway scripts, commandline hacks or in quick internal-use |
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scripts. |
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|
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By using common::sense you get a defined set of policies (ours, but maybe |
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yours, too, if you accept them), and they are easy to apply to your |
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scripts: typing C<use common::sense;> is even shorter than C<use warnings; |
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use strict; use feature ...>. |
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|
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And you can immediately use the features of your installed perl, which |
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is more difficult in code you release, but not usually an issue for |
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internal-use code (downgrades of your production perl should be rare, |
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right?). |
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|
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|
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=item mucho reduced memory usage |
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|
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Just using all those pragmas mentioned in the SYNOPSIS together wastes |
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<blink>I<< B<776> kilobytes >></blink> of precious memory in my perl, for |
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I<every single perl process using our code>, which on our machines, is a |
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lot. In comparison, this module only uses I<< B<four> >> kilobytes (I even |
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had to write it out so it looks like more) of memory on the same platform. |
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|
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The money/time/effort/electricity invested in these gigabytes (probably |
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petabytes globally!) of wasted memory could easily save 42 trees, and a |
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kitten! |
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|
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Unfortunately, until everybody applies more common sense, there will still |
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often be modules that pull in the monster pragmas. But one can hope... |
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|
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=back |
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|
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=head1 THERE IS NO 'no common::sense'!!!! !!!! !! |
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|
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This module doesn't offer an unimport. First of all, it wastes even more |
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memory, second, and more importantly, who with even a bit of common sense |
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would want no common sense? |
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|
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=head1 STABILITY AND FUTURE VERSIONS |
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|
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Future versions might change just about everything in this module. We |
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might test our modules and upload new ones working with newer versions of |
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this module, and leave you standing in the rain because we didn't tell |
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you. In fact, we did so when switching from 1.0 to 2.0, which enabled gobs |
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of warnings, and made them FATAL on top. |
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|
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Maybe we will load some nifty modules that try to emulate C<say> or so |
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with perls older than 5.10 (this module, of course, should work with older |
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perl versions - supporting 5.8 for example is just common sense at this |
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time. Maybe not in the future, but of course you can trust our common |
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sense to be consistent with, uhm, our opinion). |
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|
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=head1 WHAT OTHER PEOPLE HAD TO SAY ABOUT THIS MODULE |
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|
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apeiron |
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|
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"... wow" |
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"I hope common::sense is a joke." |
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|
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crab |
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|
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"i wonder how it would be if joerg schilling wrote perl modules." |
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|
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Adam Kennedy |
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|
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"Very interesting, efficient, and potentially something I'd use all the time." |
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[...] |
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"So no common::sense for me, alas." |
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|
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H.Merijn Brand |
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|
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"Just one more reason to drop JSON::XS from my distribution list" |
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|
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Pista Palo |
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|
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"Something in short supply these days..." |
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|
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Steffen Schwigon |
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|
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"This module is quite for sure *not* just a repetition of all the other |
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'use strict, use warnings'-approaches, and it's also not the opposite. |
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[...] And for its chosen middle-way it's also not the worst name ever. |
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And everything is documented." |
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|
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BKB |
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|
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"[Deleted - thanks to Steffen Schwigon for pointing out this review was |
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in error.]" |
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|
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Somni |
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|
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"the arrogance of the guy" |
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"I swear he tacked somenoe else's name onto the module |
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just so he could use the royal 'we' in the documentation" |
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|
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Anonymous Monk |
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|
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"You just gotta love this thing, its got META.json!!!" |
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|
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dngor |
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|
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"Heh. '"<elmex at ta-sa.org>"' The quotes are semantic |
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distancing from that e-mail address." |
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|
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Jerad Pierce |
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|
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"Awful name (not a proper pragma), and the SYNOPSIS doesn't tell you |
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anything either. Nor is it clear what features have to do with "common |
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sense" or discipline." |
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|
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acme |
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|
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"THERE IS NO 'no common::sense'!!!! !!!! !!" |
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|
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apeiron (meta-comment about us commenting^Wquoting his comment) |
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|
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"How about quoting this: get a clue, you fucktarded amoeba." |
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|
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quanth |
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|
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"common sense is beautiful, json::xs is fast, Anyevent, EV are fast and |
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furious. I love mlehmannware ;)" |
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|
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apeiron |
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|
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"... it's mlehmann's view of what common sense is. His view of common |
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sense is certainly uncommon, insofar as anyone with a clue disagrees |
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with him." |
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|
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apeiron (another meta-comment) |
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|
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"apeiron wonders if his little informant is here to steal more quotes" |
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|
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ew73 |
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|
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"... I never got past the SYNOPSIS before calling it shit." |
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[...] |
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How come no one ever quotes me. :(" |
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|
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chip (not willing to explain his cryptic questions about links in Changes files) |
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|
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"I'm willing to ask the question I've asked. I'm not willing to go |
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through the whole dance you apparently have choreographed. Either |
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answer the completely obvious question, or tell me to fuck off again." |
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|
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=head1 FREQUENTLY ASKED QUESTIONS |
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|
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Or frequently-come-up confusions. |
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|
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=over 4 |
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|
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=item Is this module meant to be serious? |
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|
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Yes, we would have put it under the C<Acme::> namespace otherwise. |
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|
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=item But the manpage is written in a funny/stupid/... way? |
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|
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This was meant to make it clear that our common sense is a subjective |
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thing and other people can use their own notions, taking the steam out |
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of anybody who might be offended (as some people are always offended no |
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matter what you do). |
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|
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This was a failure. |
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|
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But we hope the manpage still is somewhat entertaining even though it |
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explains boring rationale. |
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|
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=item Why do you impose your conventions on my code? |
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|
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For some reason people keep thinking that C<common::sense> imposes |
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process-wide limits, even though the SYNOPSIS makes it clear that it works |
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like other similar modules - i.e. only within the scope that C<use>s them. |
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|
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So, no, we don't - nobody is forced to use this module, and using a module |
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that relies on common::sense does not impose anything on you. |
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|
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=item Why do you think only your notion of common::sense is valid? |
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|
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Well, we don't, and have clearly written this in the documentation to |
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every single release. We were just faster than anybody else w.r.t. to |
| 382 |
grabbing the namespace. |
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|
| 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 |
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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 |
|
