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perldeprecation: Change some uses of "in Perl $version" to "as of Perl $version"
[perl5.git] / pod / perldeprecation.pod
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1=head1 NAME
2
3perldeprecation - list Perl deprecations
4
5=head1 DESCRIPTION
6
7The purpose of this document is to document what has been deprecated
8in Perl, and by which version the deprecated feature will disappear,
9or, for already removed features, when it was removed.
10
11This document will try to discuss what alternatives for the deprecated
12features are available.
13
14The deprecated features will be grouped by the version of Perl in
15which they will be removed.
16
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17=head2 Perl 5.32
18
19=head3 Constants from lexical variables potentially modified elsewhere
20
21You wrote something like
22
23 my $var;
24 $sub = sub () { $var };
25
26but $var is referenced elsewhere and could be modified after the C<sub>
27expression is evaluated. Either it is explicitly modified elsewhere
28(C<$var = 3>) or it is passed to a subroutine or to an operator like
29C<printf> or C<map>, which may or may not modify the variable.
30
31Traditionally, Perl has captured the value of the variable at that
32point and turned the subroutine into a constant eligible for inlining.
33In those cases where the variable can be modified elsewhere, this
34breaks the behavior of closures, in which the subroutine captures
35the variable itself, rather than its value, so future changes to the
36variable are reflected in the subroutine's return value.
37
38If you intended for the subroutine to be eligible for inlining, then
39make sure the variable is not referenced elsewhere, possibly by
40copying it:
41
42 my $var2 = $var;
43 $sub = sub () { $var2 };
44
45If you do want this subroutine to be a closure that reflects future
46changes to the variable that it closes over, add an explicit C<return>:
47
48 my $var;
49 $sub = sub () { return $var };
50
51This usage has been deprecated, and will no longer be allowed in Perl 5.32.
52
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53=head2 Use of strings with code points over 0xFF as arguments to C<vec>
54
55C<vec> views its string argument as a sequence of bits. A string
56containing a code point over 0xFF is nonsensical. This usage is
57deprecated in Perl 5.28, and will be removed in Perl 5.32.
58
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59=head2 Perl 5.30
60
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61=head3 C<< $* >> is no longer supported
62
63Before Perl 5.10, setting C<< $* >> to a true value globally enabled
64multi-line matching within a string. This relique from the past lost
65its special meaning in 5.10. Use of this variable will be a fatal error
66in Perl 5.30, freeing the variable up for a future special meaning.
67
68To enable multiline matching one should use the C<< /m >> regexp
69modifier (possibly in combination with C<< /s >>). This can be set
70on a per match bases, or can be enabled per lexical scope (including
71a whole file) with C<< use re '/m' >>.
72
73=head3 C<< $# >> is no longer supported
74
75This variable used to have a special meaning -- it could be used
76to control how numbers were formatted when printed. This seldom
77used functionality was removed in Perl 5.10. In order to free up
78the variable for a future special meaning, its use will be a fatal
79error in Perl 5.30.
80
81To specify how numbers are formatted when printed, one is adviced
82to use C<< printf >> or C<< sprintf >> instead.
83
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84=head3 C<< File::Glob::glob() >> will disappear
85
86C<< File::Glob >> has a function called C<< glob >>, which just calls
87C<< bsd_glob >>. However, its prototype is different from the prototype
88of C<< CORE::glob >>, and hence, C<< File::Glob::glob >> should not
89be used.
90
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91C<< File::Glob::glob() >> was deprecated in Perl 5.8. A deprecation
92message was issued from Perl 5.26 onwards, and the function will
93disappear in Perl 5.30.
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94
95Code using C<< File::Glob::glob() >> should call
96C<< File::Glob::bsd_glob() >> instead.
97
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98
99=head3 Unescaped left braces in regular expressions
100
101The simple rule to remember, if you want to match a literal C<{>
102character (U+007B C<LEFT CURLY BRACKET>) in a regular expression
103pattern, is to escape each literal instance of it in some way.
104Generally easiest is to precede it with a backslash, like C<\{>
105or enclose it in square brackets (C<[{]>). If the pattern
106delimiters are also braces, any matching right brace (C<}>) should
107also be escaped to avoid confusing the parser, for example,
108
109 qr{abc\{def\}ghi}
110
111Forcing literal C<{> characters to be escaped will enable the Perl
112language to be extended in various ways in future releases. To avoid
113needlessly breaking existing code, the restriction is is not enforced in
114contexts where there are unlikely to ever be extensions that could
115conflict with the use there of C<{> as a literal.
116
117Literal uses of C<{> were deprecated in Perl 5.20, and some uses of it
118started to give deprecation warnings since. These cases were made fatal
119in Perl 5.26. Due to an oversight, not all cases of a use of a literal
120C<{> got a deprecation warning. These cases started warning in Perl 5.26,
121and they will be fatal by Perl 5.30.
122
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123=head3 Unqualified C<dump()>
124
125Use of C<dump()> instead of C<CORE::dump()> was deprecated in Perl 5.8,
126and an unqualified C<dump()> will no longer be available in Perl 5.30.
127
128See L<perlfunc/dump>.
129
286c9456 130
afb5c82e 131=head3 Using my() in false conditional.
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132
133There has been a long-standing bug in Perl that causes a lexical variable
134not to be cleared at scope exit when its declaration includes a false
135conditional. Some people have exploited this bug to achieve a kind of
136static variable. Since we intend to fix this bug, we don't want people
137relying on this behavior.
138
139Instead, it's recommended one uses C<state> variables to achieve the
140same effect:
141
142 use 5.10.0;
143 sub count {state $counter; return ++ $counter}
144 say count (); # Prints 1
145 say count (); # Prints 2
146
147C<state> variables were introduced in Perl 5.10.
148
149Alternatively, you can achieve a similar static effect by
150declaring the variable in a separate block outside the function, eg
151
152 sub f { my $x if 0; return $x++ }
153
154becomes
155
156 { my $x; sub f { return $x++ } }
157
158The use of C<my()> in a false conditional has been deprecated in
159Perl 5.10, and it will become a fatal error in Perl 5.30.
160
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161
162=head3 Reading/writing bytes from/to :utf8 handles.
163
164The sysread(), recv(), syswrite() and send() operators are
165deprecated on handles that have the C<:utf8> layer, either explicitly, or
166implicitly, eg., with the C<:encoding(UTF-16LE)> layer.
167
168Both sysread() and recv() currently use only the C<:utf8> flag for the stream,
169ignoring the actual layers. Since sysread() and recv() do no UTF-8
170validation they can end up creating invalidly encoded scalars.
171
172Similarly, syswrite() and send() use only the C<:utf8> flag, otherwise ignoring
173any layers. If the flag is set, both write the value UTF-8 encoded, even if
174the layer is some different encoding, such as the example above.
175
176Ideally, all of these operators would completely ignore the C<:utf8> state,
177working only with bytes, but this would result in silently breaking existing
178code. To avoid this a future version of perl will throw an exception when
179any of sysread(), recv(), syswrite() or send() are called on handle with the
180C<:utf8> layer.
181
182In Perl 5.30, it will no longer be possible to use sysread(), recv(),
183syswrite() or send() to read or send bytes from/to :utf8 handles.
184
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185
186=head3 Use of unassigned code point or non-standalone grapheme for a delimiter.
187
188A grapheme is what appears to a native-speaker of a language to be a
189character. In Unicode (and hence Perl) a grapheme may actually be
190several adjacent characters that together form a complete grapheme. For
191example, there can be a base character, like "R" and an accent, like a
192circumflex "^", that appear when displayed to be a single character with
193the circumflex hovering over the "R". Perl currently allows things like
194that circumflex to be delimiters of strings, patterns, I<etc>. When
195displayed, the circumflex would look like it belongs to the character
196just to the left of it. In order to move the language to be able to
197accept graphemes as delimiters, we have to deprecate the use of
198delimiters which aren't graphemes by themselves. Also, a delimiter must
199already be assigned (or known to be never going to be assigned) to try
200to future-proof code, for otherwise code that works today would fail to
201compile if the currently unassigned delimiter ends up being something
202that isn't a stand-alone grapheme. Because Unicode is never going to
203assign
204L<non-character code points|perlunicode/Noncharacter code points>, nor
205L<code points that are above the legal Unicode maximum|
206perlunicode/Beyond Unicode code points>, those can be delimiters, and
207their use won't raise this warning.
208
209In Perl 5.30, delimiters which are unassigned code points, or which
210are non-standalone graphemes will be fatal.
211
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212=head3 In XS code, use of various macros dealing with UTF-8.
213
214These macros will require an extra parameter in Perl 5.30:
215C<isALPHANUMERIC_utf8>,
216C<isASCII_utf8>,
217C<isBLANK_utf8>,
218C<isCNTRL_utf8>,
219C<isDIGIT_utf8>,
220C<isIDFIRST_utf8>,
221C<isPSXSPC_utf8>,
222C<isSPACE_utf8>,
223C<isVERTWS_utf8>,
224C<isWORDCHAR_utf8>,
225C<isXDIGIT_utf8>,
226C<isALPHANUMERIC_LC_utf8>,
227C<isALPHA_LC_utf8>,
228C<isASCII_LC_utf8>,
229C<isBLANK_LC_utf8>,
230C<isCNTRL_LC_utf8>,
231C<isDIGIT_LC_utf8>,
232C<isGRAPH_LC_utf8>,
233C<isIDCONT_LC_utf8>,
234C<isIDFIRST_LC_utf8>,
235C<isLOWER_LC_utf8>,
236C<isPRINT_LC_utf8>,
237C<isPSXSPC_LC_utf8>,
238C<isPUNCT_LC_utf8>,
239C<isSPACE_LC_utf8>,
240C<isUPPER_LC_utf8>,
241C<isWORDCHAR_LC_utf8>,
242C<isXDIGIT_LC_utf8>,
243C<toFOLD_utf8>,
244C<toLOWER_utf8>,
245C<toTITLE_utf8>,
246and
247C<toUPPER_utf8>.
248
249There is now a macro that corresponds to each one of these, simply by
250appending C<_safe> to the name. It takes the extra parameter.
251For example, C<isDIGIT_utf8_safe> corresponds to C<isDIGIT_utf8>, but
252takes the extra parameter, and its use doesn't generate a deprecation
253warning. All are documented in L<perlapi/Character case changing> and
254L<perlapi/Character classification>.
255
256You can change to use these versions at any time, or, if you can live
257with the deprecation messages, wait until 5.30 and add the parameter to
258the existing calls, without changing the names.
30573109 259
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260=head2 Perl 5.28
261
dcc013e3 262=head3 Attributes C<< :locked >> and C<< :unique >>
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263
264The attributes C<< :locked >> (on code references) and C<< :unique >>
265(on array, hash and scalar references) have had no effect since
266Perl 5.005 and Perl 5.8.8 respectively. Their use has been deprecated
267since.
268
d1f1f359 269As of Perl 5.28, these attributes are syntax errors. Since the
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270attributes do not do anything, removing them from your code fixes
271the syntax error; and removing them will not influence the behaviour
272of your code.
c9680906 273
ac641426 274
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275=head3 Bare here-document terminators
276
277Perl has allowed you to use a bare here-document terminator to have the
278here-document end at the first empty line. This practise was deprecated
d1f1f359 279in Perl 5.000; as of Perl 5.28, using a bare here-document terminator
dcc013e3 280throws a fatal error.
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281
282You are encouraged to use the explictly quoted form if you wish to
283use an empty line as the terminator of the here-document:
284
285 print <<"";
286 Print this line.
287
288 # Previous blank line ends the here-document.
289
290
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291=head3 Setting $/ to a reference to a non-positive integer
292
293You assigned a reference to a scalar to C<$/> where the
294referenced item is not a positive integer. In older perls this B<appeared>
295to work the same as setting it to C<undef> but was in fact internally
296different, less efficient and with very bad luck could have resulted in
297your file being split by a stringified form of the reference.
298
299In Perl 5.20.0 this was changed so that it would be B<exactly> the same as
300setting C<$/> to undef, with the exception that this warning would be
301thrown.
302
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303As of Perl 5.28, setting C<$/> to a reference of a non-positive
304integer throws a fatal error.
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305
306You are recommended to change your code to set C<$/> to C<undef> explicitly
307if you wish to slurp the file.
308
309
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310=head3 Limit on the value of Unicode code points.
311
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312Unicode only allows code points up to 0x10FFFF, but Perl allows
313much larger ones. Up till Perl 5.28, it was allowed to use code
314points exceeding the maximum value of an integer (C<IV_MAX>).
315However, that did break the perl interpreter in some constructs,
316including causing it to hang in a few cases. The known problem
317areas were in C<tr///>, regular expression pattern matching using
318quantifiers, as quote delimiters in C<qI<X>...I<X>> (where I<X> is
319the C<chr()> of a large code point), and as the upper limits in
320loops.
fcdb3ac1 321
d1f1f359 322The use of out of range code points was deprecated in Perl 5.24; as of
dcc013e3 323Perl 5.28 using a code point exceeding C<IV_MAX> throws a fatal error.
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324
325If your code is to run on various platforms, keep in mind that the upper
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326limit depends on the platform. It is much larger on 64-bit word sizes
327than 32-bit ones. For 32-bit integers, C<IV_MAX> equals C<0x7FFFFFFF>,
328for 64-bit integers, C<IV_MAX> equals C<0x7FFFFFFFFFFFFFFF>.
fcdb3ac1 329
db99d38d 330
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331=head3 Use of comma-less variable list in formats.
332
dcc013e3 333It was allowed to use a list of variables in a format, without
6ef4f8b7 334separating them with commas. This usage has been deprecated
d1f1f359 335for a long time, and as of Perl 5.28, this throws a fatal error.
6ef4f8b7 336
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337=head3 Use of C<\N{}>
338
339Use of C<\N{}> with nothing between the braces was deprecated in
be332ba0 340Perl 5.24, and throws a fatal error as of Perl 5.28.
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341
342Since such a construct is equivalent to using an empty string,
343you are recommended to remove such C<\N{}> constructs.
344
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345=head3 Using the same symbol to open a filehandle and a dirhandle
346
347It used to be legal to use C<open()> to associate both a
348filehandle and a dirhandle to the same symbol (glob or scalar).
349This idiom is likely to be confusing, and it was deprecated in
350Perl 5.10.
351
352Using the same symbol to C<open()> a filehandle and a dirhandle
d1f1f359 353throws a fatal error as of Perl 5.28.
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354
355You should be using two different symbols instead.
356
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357=head3 ${^ENCODING} is no longer supported.
358
359The special variable C<${^ENCODING}> was used to implement
360the C<encoding> pragma. Setting this variable to anything other
361than C<undef> was deprecated in Perl 5.22. Full deprecation
362of the variable happened in Perl 5.25.3.
363
dcc013e3 364Setting this variable to anything other than an undefined value
d1f1f359 365throws a fatal error as of Perl 5.28.
ac641426 366
d9d53e86 367
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368=head3 C<< B::OP::terse >>
369
370This method, which just calls C<< B::Concise::b_terse >>, has been
dcc013e3 371deprecated, and disappeared in Perl 5.28. Please use
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372C<< B::Concise >> instead.
373
374
d9d53e86 375
dcc013e3 376=head3 Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
d9d53e86 377
dcc013e3 378As an (ahem) accidental feature, C<AUTOLOAD> subroutines were looked
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379up as methods (using the C<@ISA> hierarchy) even when the subroutines
380to be autoloaded were called as plain functions (e.g. C<Foo::bar()>),
381not as methods (e.g. C<< Foo->bar() >> or C<< $obj->bar() >>).
382
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383This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28
384by using method lookup only for methods' C<AUTOLOAD>s.
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385
386The simple rule is: Inheritance will not work when autoloading
387non-methods. The simple fix for old code is: In any module that used
388to depend on inheriting C<AUTOLOAD> for non-methods from a base class
389named C<BaseClass>, execute C<*AUTOLOAD = \&BaseClass::AUTOLOAD> during
390startup.
391
392In code that currently says C<use AutoLoader; @ISA = qw(AutoLoader);>
393you should remove AutoLoader from @ISA and change C<use AutoLoader;> to
394C<use AutoLoader 'AUTOLOAD';>.
395
d9d53e86 396
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397=head3 Use of code points over 0xFF in string bitwise operators
398
399The string bitwise operators, C<&>, C<|>, C<^>, and C<~>, treat
400their operands as strings of bytes. As such, values above 0xFF
401are nonsensical. Using such code points with these operators
d1f1f359 402was deprecated in Perl 5.24, and is fatal as of Perl 5.28.
ecbcbef0 403
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404=head3 In XS code, use of C<to_utf8_case()>
405
f566c7cf 406This function has been removed as of Perl 5.28; instead convert to call
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407the appropriate one of:
408L<C<toFOLD_utf8_safe>|perlapi/toFOLD_utf8_safe>.
409L<C<toLOWER_utf8_safe>|perlapi/toLOWER_utf8_safe>,
410L<C<toTITLE_utf8_safe>|perlapi/toTITLE_utf8_safe>,
411or
412L<C<toUPPER_utf8_safe>|perlapi/toUPPER_utf8_safe>.
bfdc8cd3 413
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414=head2 Perl 5.26
415
416=head3 C<< --libpods >> in C<< Pod::Html >>
417
418Since Perl 5.18, the option C<< --libpods >> has been deprecated, and
419using this option did not do anything other than producing a warning.
420
d1f1f359 421The C<< --libpods >> option is no longer recognized as of Perl 5.26.
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422
423
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424=head3 The utilities C<< c2ph >> and C<< pstruct >>
425
426These old, perl3-era utilities have been deprecated in favour of
d1f1f359 427C<< h2xs >> for a long time. As of Perl 5.26, they have been removed.
2560602c 428
d9d53e86 429
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430=head3 Trapping C<< $SIG {__DIE__} >> other than during program exit.
431
432The C<$SIG{__DIE__}> hook is called even inside an C<eval()>. It was
433never intended to happen this way, but an implementation glitch made
434this possible. This used to be deprecated, as it allowed strange action
435at a distance like rewriting a pending exception in C<$@>. Plans to
436rectify this have been scrapped, as users found that rewriting a
437pending exception is actually a useful feature, and not a bug.
438
439Perl never issued a deprecation warning for this; the deprecation
440was by documentation policy only. But this deprecation has been
d1f1f359 441lifted as of Perl 5.26.
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442
443
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444=head3 Malformed UTF-8 string in "%s"
445
446This message indicates a bug either in the Perl core or in XS
447code. Such code was trying to find out if a character, allegedly
448stored internally encoded as UTF-8, was of a given type, such as
449being punctuation or a digit. But the character was not encoded
450in legal UTF-8. The C<%s> is replaced by a string that can be used
451by knowledgeable people to determine what the type being checked
452against was.
453
454Passing malformed strings was deprecated in Perl 5.18, and
455became fatal in Perl 5.26.
456
457
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458=head2 Perl 5.24
459
460=head3 Use of C<< *glob{FILEHANDLE} >>
461
d1be68f6 462The use of C<< *glob{FILEHANDLE} >> was deprecated in Perl 5.8.
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463The intention was to use C<< *glob{IO} >> instead, for which
464C<< *glob{FILEHANDLE} >> is an alias.
465
d1be68f6 466However, this feature was undeprecated in Perl 5.24.
9021a1cf 467
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468=head3 Calling POSIX::%s() is deprecated
469
470The following functions in the C<POSIX> module are no longer available:
471C<isalnum>, C<isalpha>, C<iscntrl>, C<isdigit>, C<isgraph>, C<islower>,
472C<isprint>, C<ispunct>, C<isspace>, C<isupper>, and C<isxdigit>. The
473functions are buggy and don't work on UTF-8 encoded strings. See their
474entries in L<POSIX> for more information.
475
d1be68f6 476The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
46d7f3c1
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477
478
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479=head2 Perl 5.16
480
481=head3 Use of %s on a handle without * is deprecated
482
483It used to be possible to use C<tie>, C<tied> or C<untie> on a scalar
484while the scalar holds a typeglob. This caused its filehandle to be
485tied. It left no way to tie the scalar itself when it held a typeglob,
486and no way to untie a scalar that had had a typeglob assigned to it.
487
d1be68f6 488This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
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489
490So now C<tie $scalar> will always tie the scalar, not the handle it holds.
491To tie the handle, use C<tie *$scalar> (with an explicit asterisk). The same
492applies to C<tied *$scalar> and C<untie *$scalar>.
493
494
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495=head1 SEE ALSO
496
497L<warnings>, L<diagnostics>.
498
499=cut