5 $unicode8bit::hint_uni8bit = 0x00000800;
8 "5.10" => [qw(unicode8bit)],
9 "5.11" => [qw(unicode8bit)],
12 my %legacy = ( 'unicode8bit' => '0' );
16 legacy - Perl pragma to preserve legacy behaviors or enable new non-default
21 use legacy ':5.10'; # Keeps semantics the same as in perl 5.10
23 use legacy qw(unicode8bit);
27 no legacy qw(unicode8bit);
31 Some programs may rely on behaviors that for others are problematic or
32 even wrong. A new version of Perl may change behaviors from past ones,
33 and when it is viewed that the old way of doing things may be required
34 to still be supported, the new behavior will be able to be turned off by using
37 Additionally, a new behavior may be supported in a new version of Perl, but
38 for whatever reason the default remains the old one. This pragma can enable
41 Like other pragmas (C<use feature>, for example), C<use legacy qw(foo)> will
42 only make the legacy behavior for "foo" available from that point to the end of
47 Preserve the old way of doing things when a new version of Perl is
48 released that would otherwise change the behavior.
50 The one current possibility is:
54 THIS IS SUBJECT TO CHANGE
56 Use legacy semantics for the 128 characters on ASCII systems that have the 8th
57 bit set. (See L</EBCDIC platforms> below for EBCDIC systems.) Unless
58 C<S<use locale>> is specified, or the scalar containing such a character is
59 known by Perl to be encoded in UTF8, the semantics are essentially that the
60 characters have an ordinal number, and that's it. They are caseless, and
61 aren't anything: they're not controls, not letters, not punctuation, ..., not
64 This behavior stems from when Perl did not support Unicode, and ASCII was the
65 only known character set outside of C<S<use locale>>. In order to not
66 possibly break pre_Unicode programs, these characters have retained their old
67 non-meanings, except when it is clear to Perl that Unicode is what is meant,
68 for example by calling utf::upgrade() on a scalar, or if the scalar also
69 contains characters that are only available in Unicode. Then these 128
70 characters take on their Unicode meanings.
72 The problem with this behavior is that a scalar that encodes these characters
73 has a different meaning depending on if it is stored as utf8 or not.
74 In general, the internal storage method should not affect the
77 The behavior is known to have effects on these areas:
83 Changing the case of a scalar, that is, using C<uc()>,
86 and C<lcfirst()>, or C<\L>, C<\U>, C<\u> and C<\l> in regular expression substitutions.
90 Using caseless (C</i>) regular expression matching
94 Matching a number of properties in regular expressions, such as C<\w>
98 User-defined case change mappings. You can create a C<ToUpper()> function, for
99 example, which overrides Perl's built-in case mappings. The scalar must be
100 encoded in utf8 for your function to actually be invoked.
104 B<This lack of semantics for these characters is currently the default,>
105 outside of C<use locale>. See below for EBCDIC.
106 To turn on B<case changing semantics only> for these characters, use
108 The other legacy behaviors regarding these characters are currently
109 unaffected by this pragma.
111 =head4 EBCDIC platforms
113 On EBCDIC platforms, the situation is somewhat different. The legacy
114 semantics are whatever the underlying semantics of the native C language
115 library are. Each of the three EBCDIC encodings currently known by Perl is an
116 isomorph of the Latin-1 character set. That means every character in Latin-1
117 has a corresponding EBCDIC equivalent, and vice-versa. Specifying C<S<no
118 legacy>> currently makes sure that all EBCDIC characters have the same
119 B<casing only> semantics as their corresponding Latin-1 characters.
123 Turn on a new behavior in a version of Perl that understands
124 it but has it turned off by default. For example, C<no legacy 'foo'> turns on
125 behavior C<foo> in the lexical scope of the pragma. C<no legacy>
126 without any modifier turns on all new behaviors known to the pragma.
128 =head1 LEGACY BUNDLES
130 It's possible to turn off all new behaviors past a given release by
131 using a I<legacy bundle>, which is the name of the release prefixed with
132 a colon, to distinguish it from an individual legacy behavior.
134 Specifying sub-versions such as the C<0> in C<5.10.0> in legacy bundles has
135 no effect: legacy bundles are guaranteed to be the same for all sub-versions.
137 Legacy bundles are not allowed with C<no legacy>
144 croak("No legacy behaviors specified");
147 my $name = shift(@_);
148 if (substr($name, 0, 1) eq ":") {
149 my $v = substr($name, 1);
150 if (!exists $legacy_bundle{$v}) {
151 $v =~ s/^([0-9]+)\.([0-9]+).[0-9]+$/$1.$2/;
152 if (!exists $legacy_bundle{$v}) {
153 unknown_legacy_bundle(substr($name, 1));
156 unshift @_, @{$legacy_bundle{$v}};
159 if (!exists $legacy{$name}) {
160 unknown_legacy($name);
162 $^H &= ~$unicode8bit::hint_uni8bit; # The only valid thing as of yet
170 # A bare C<no legacy> should disable *all* legacy behaviors
172 unshift @_, keys(%legacy);
177 if (substr($name, 0, 1) eq ":") {
178 croak(sprintf('Legacy bundles (%s) are not allowed in "no legacy"',
181 if (!exists($legacy{$name})) {
182 unknown_legacy($name);
185 $^H |= $unicode8bit::hint_uni8bit; # The only valid thing as of yet
192 croak(sprintf('Legacy "%s" is not supported by Perl %vd', $legacy, $^V));
195 sub unknown_legacy_bundle {
197 croak(sprintf('Legacy bundle "%s" is not supported by Perl %vd',