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 evaluated in boolean context,
24 following their usual semantics; see L<perlop/"Range Operators">.
26 =item defined-or operator
28 A compound expression involving the defined-or operator, as in
29 C<when (expr1 // expr2)>, will be treated as boolean if the first
30 expression is boolean. (This just extends the existing rule that applies
31 to the regular or operator, as in C<when (expr1 || expr2)>.)
35 The next paragraph details more changes brought to the semantics to
36 the smart match operator, that naturally also modify the behaviour
37 of the switch statements where smart matching is implicitly used.
39 =head2 Smart match changes
41 =head3 Changes to type-based dispatch
43 The smart match operator C<~~> is no longer commutative. The behaviour of
44 a smart match now depends primarily on the type of its right hand
45 argument. Moreover, its semantics has been adjusted for greater
46 consistency or usefulness in several cases. While the general backwards
47 compatibility is maintained, several changes must be noted:
53 Code references with an empty prototype are no longer treated specially.
54 They are passed an argument like the other code references (even if they
59 C<%hash ~~ sub {}> and C<@array ~~ sub {}> now test that the subroutine
60 returns a true value for each key of the hash (or element of the
61 array), instead of passing the whole hash or array as a reference to
66 Due to the commutativity breakage, code references are no longer
67 treated specially when appearing on the left of the C<~~> operator,
68 but like any vulgar scalar.
72 C<undef ~~ %hash> is always false (since C<undef> can't be a key in a
73 hash). No implicit conversion to C<""> is done (as was the case in perl
78 C<$scalar ~~ @array> now always distributes the smart match across the
79 elements of the array. It's true if one element in @array verifies
80 C<$scalar ~~ $element>. This is a generalization of the old behaviour
81 that tested whether the array contained the scalar.
85 The full dispatch table for the smart match operator is given in
86 L<perlsyn/"Smart matching in detail">.
88 =head3 Smart match and overloading
90 According to the rule of dispatch based on the rightmost argument type,
91 when an object overloading C<~~> appears on the right side of the
92 operator, the overload routine will always be called (with a 3rd argument
93 set to a true value, see L<overload>.) However, when the object will
94 appear on the left, the overload routine will be called only when the
95 rightmost argument is a simple scalar. This way distributivity of smart match
96 across arrays is not broken, as well as the other behaviours with complex
97 types (coderefs, hashes, regexes). Thus, writers of overloading routines
98 for smart match mostly need to worry only with comparing against a scalar,
99 and possibly with stringification overloading; the other common cases
100 will be automatically handled consistently.
102 C<~~> will now refuse to work on objects that do not overload it (in order
103 to avoid relying on the object's underlying structure).
105 =head1 Core Enhancements
107 =head1 The C<overloading> pragma
109 This pragma allows you to lexically disable or enable overloading
110 for some or all operations. (Yuval Kogman)
112 =head1 Modules and Pragmata
114 =head2 Pragmata Changes
120 See L</"The C<overloading> pragma"> above.
124 =head1 Utility Changes
128 =head1 Performance Enhancements
130 =head1 Installation and Configuration Improvements
132 =head1 Selected Bug Fixes
136 =item C<-I> on shebang line now adds directories in front of @INC
138 as documented, and as does C<-I> when specified on the command-line.
143 =head1 New or Changed Diagnostics
145 =head1 Changed Internals
147 =head1 Known Problems
149 =head2 Platform Specific Problems
151 =head1 Reporting Bugs
153 If you find what you think is a bug, you might check the articles
154 recently posted to the comp.lang.perl.misc newsgroup and the perl
155 bug database at http://bugs.perl.org/ . There may also be
156 information at http://www.perl.org/ , the Perl Home Page.
158 If you believe you have an unreported bug, please run the B<perlbug>
159 program included with your release. Be sure to trim your bug down
160 to a tiny but sufficient test case. Your bug report, along with the
161 output of C<perl -V>, will be sent off to perlbug@perl.org to be
162 analysed by the Perl porting team.
166 The F<Changes> file for exhaustive details on what changed.
168 The F<INSTALL> file for how to build Perl.
170 The F<README> file for general stuff.
172 The F<Artistic> and F<Copying> files for copyright information.