3 perldelta - what is new for perl v5.11.0
7 This document describes differences between the 5.10.0 and the 5.11.0
10 =head1 Incompatible Changes
12 =head2 Switch statement changes
14 The handling of complex expressions by the C<given>/C<when> switch
15 statement has been enhanced. There are two new cases where C<when> now
16 interprets its argument as a boolean, instead of an expression to be used
21 =item flip-flop operators
23 The C<..> and C<...> flip-flop operators are now evaluated in boolean
24 context, following their usual semantics; see L<perlop/"Range Operators">.
26 Note that, as in perl 5.10.0, C<when (1..10)> will not work to test
27 whether a given value is an integer between 1 and 10; you should use
28 C<when ([1..10])> instead (note the array reference).
30 However, contrary to 5.10.0, evaluating the flip-flop operators in boolean
31 context ensures it can now be useful in a C<when()>, notably for
32 implementing bistable conditions, like in:
34 when (/^=begin/ .. /^=end/) { ... }
36 =item defined-or operator
38 A compound expression involving the defined-or operator, as in
39 C<when (expr1 // expr2)>, will be treated as boolean if the first
40 expression is boolean. (This just extends the existing rule that applies
41 to the regular or operator, as in C<when (expr1 || expr2)>.)
45 The next section details more changes brought to the semantics to
46 the smart match operator, that naturally also modify the behaviour
47 of the switch statements where smart matching is implicitly used.
49 =head2 Smart match changes
51 =head3 Changes to type-based dispatch
53 The smart match operator C<~~> is no longer commutative. The behaviour of
54 a smart match now depends primarily on the type of its right hand
55 argument. Moreover, its semantics has been adjusted for greater
56 consistency or usefulness in several cases. While the general backwards
57 compatibility is maintained, several changes must be noted:
63 Code references with an empty prototype are no longer treated specially.
64 They are passed an argument like the other code references (even if they
69 C<%hash ~~ sub {}> and C<@array ~~ sub {}> now test that the subroutine
70 returns a true value for each key of the hash (or element of the
71 array), instead of passing the whole hash or array as a reference to
76 Due to the commutativity breakage, code references are no longer
77 treated specially when appearing on the left of the C<~~> operator,
78 but like any vulgar scalar.
82 C<undef ~~ %hash> is always false (since C<undef> can't be a key in a
83 hash). No implicit conversion to C<""> is done (as was the case in perl
88 C<$scalar ~~ @array> now always distributes the smart match across the
89 elements of the array. It's true if one element in @array verifies
90 C<$scalar ~~ $element>. This is a generalization of the old behaviour
91 that tested whether the array contained the scalar.
95 The full dispatch table for the smart match operator is given in
96 L<perlsyn/"Smart matching in detail">.
98 =head3 Smart match and overloading
100 According to the rule of dispatch based on the rightmost argument type,
101 when an object overloading C<~~> appears on the right side of the
102 operator, the overload routine will always be called (with a 3rd argument
103 set to a true value, see L<overload>.) However, when the object will
104 appear on the left, the overload routine will be called only when the
105 rightmost argument is a simple scalar. This way distributivity of smart match
106 across arrays is not broken, as well as the other behaviours with complex
107 types (coderefs, hashes, regexes). Thus, writers of overloading routines
108 for smart match mostly need to worry only with comparing against a scalar,
109 and possibly with stringification overloading; the other common cases
110 will be automatically handled consistently.
112 C<~~> will now refuse to work on objects that do not overload it (in order
113 to avoid relying on the object's underlying structure). (However, if the
114 object overloads the stringification or the numification operators, and
115 if overload fallback is active, it will be used instead, as usual.)
117 =head1 Core Enhancements
119 =head2 The C<overloading> pragma
121 This pragma allows you to lexically disable or enable overloading
122 for some or all operations. (Yuval Kogman)
124 =head2 C<\N> regex escape
126 A new regex escape has been added, C<\N>. It will match any character that
127 is not a newline, independently from the presence or absence of the single
128 line match modifier C</s>. (If C<\N> is followed by an opening brace and
129 by a letter, perl will still assume that a Unicode character name is
130 coming, so compatibility is preserved.) (Rafael Garcia-Suarez)
132 =head2 Implicit strictures
134 Using the C<use VERSION> syntax with a version number greater or equal
135 to 5.11.0 will also lexically enable strictures just like C<use strict>
136 would do (in addition to enabling features.) So, the following:
145 =head2 Parallel tests
147 The core distribution can now run its regression tests in parallel on
148 Unix-like platforms. Instead of running C<make test>, set C<TEST_JOBS> in
149 your environment to the number of tests to run in parallel, and run
150 C<make test_harness>. On a Bourne-like shell, this can be done as
152 TEST_JOBS=3 make test_harness # Run 3 tests in parallel
154 An environment variable is used, rather than parallel make itself, because
155 L<TAP::Harness> needs to be able to schedule individual non-conflicting test
156 scripts itself, and there is no standard interface to C<make> utilities to
157 interact with their job schedulers.
159 =head2 The C<...> operator
161 A new operator, C<...>, nicknamed the Yada Yada operator, has been added.
162 It is intended to mark placeholder code, that is not yet implemented.
163 See L<perlop/"Yada Yada Operator">. (chromatic)
165 =head1 Modules and Pragmata
167 =head2 Pragmata Changes
173 See L</"The C<overloading> pragma"> above.
177 =head2 Selected Changes to Core Modules
181 L<Carp> now includes all the necessary code to function. Previously, it
182 used to be a lightweight placeholder that loaded the actual code from
183 C<Carp::Heavy> on demand. C<Carp::Heavy> is now a simple, empty module
184 kept for backwards compatibility for programs that used to pre-load it.
188 =head1 Utility Changes
192 =head1 Performance Enhancements
194 =head1 Installation and Configuration Improvements
196 =head1 Selected Bug Fixes
200 =item C<-I> on shebang line now adds directories in front of @INC
202 as documented, and as does C<-I> when specified on the command-line.
205 =item C<kill> is now fatal when called on non-numeric process identifiers
207 Previously, an 'undef' process identifier would be interpreted as a request to
208 kill process "0", which would terminate the current process group on POSIX
209 systems. Since process identifiers are always integers, killing a non-numeric
210 process is now fatal.
212 =item C<-C> on the shebang line is once more permitted
214 if it is also specified on the command line. C<-C> on the shebang line used
215 to be a silent no-op I<if> it was not also on the command line, so perl
216 5.10.0 disallowed it, which broke some scripts. Now perl checks whether it
217 is also on the command line and only dies if it is not.
221 =head1 New or Changed Diagnostics
223 =head1 Changed Internals
225 =head1 Known Problems
227 =head2 Platform Specific Problems
229 =head1 Reporting Bugs
231 If you find what you think is a bug, you might check the articles
232 recently posted to the comp.lang.perl.misc newsgroup and the perl
233 bug database at http://bugs.perl.org/ . There may also be
234 information at http://www.perl.org/ , the Perl Home Page.
236 If you believe you have an unreported bug, please run the B<perlbug>
237 program included with your release. Be sure to trim your bug down
238 to a tiny but sufficient test case. Your bug report, along with the
239 output of C<perl -V>, will be sent off to perlbug@perl.org to be
240 analysed by the Perl porting team.
242 If the bug you are reporting has security implications, which make it
243 inappropriate to send to a publicly archived mailing list, then please send
244 it to perl5-security-report@perl.org. This points to a closed subscription
245 unarchived mailing list, which includes all the core committers, who be able
246 to help assess the impact of issues, figure out a resolution, and help
247 co-ordinate the release of patches to mitigate or fix the problem across all
248 platforms on which Perl is supported. Please only use this address for security
249 issues in the Perl core, not for modules independently distributed on CPAN.
253 The F<Changes> file for exhaustive details on what changed.
255 The F<INSTALL> file for how to build Perl.
257 The F<README> file for general stuff.
259 The F<Artistic> and F<Copying> files for copyright information.