perldeprecation - list Perl deprecations
The purpose of this document is to document what has been deprecated in Perl, and by which version the deprecated feature will disappear, or, for already removed features, when it was removed.
This document will try to discuss what alternatives for the deprecated features are available.
The deprecated features will be grouped by the version of Perl in which they will be removed.
You wrote something like
- my $var;
- $sub = sub () { $var };
but $var is referenced elsewhere and could be modified after the sub
expression is evaluated. Either it is explicitly modified elsewhere
($var = 3
) or it is passed to a subroutine or to an operator like
printf or map, which may or may not modify the variable.
Traditionally, Perl has captured the value of the variable at that point and turned the subroutine into a constant eligible for inlining. In those cases where the variable can be modified elsewhere, this breaks the behavior of closures, in which the subroutine captures the variable itself, rather than its value, so future changes to the variable are reflected in the subroutine's return value.
If you intended for the subroutine to be eligible for inlining, then make sure the variable is not referenced elsewhere, possibly by copying it:
- my $var2 = $var;
- $sub = sub () { $var2 };
If you do want this subroutine to be a closure that reflects future
changes to the variable that it closes over, add an explicit return:
This usage has been deprecated, and will no longer be allowed in Perl 5.32.
$*
is no longer supportedBefore Perl 5.10, setting $*
to a true value globally enabled
multi-line matching within a string. This relique from the past lost
its special meaning in 5.10. Use of this variable will be a fatal error
in Perl 5.30, freeing the variable up for a future special meaning.
To enable multiline matching one should use the /m regexp
modifier (possibly in combination with /s). This can be set
on a per match bases, or can be enabled per lexical scope (including
a whole file) with use re '/m'
.
$#
is no longer supportedThis variable used to have a special meaning -- it could be used to control how numbers were formatted when printed. This seldom used functionality was removed in Perl 5.10. In order to free up the variable for a future special meaning, its use will be a fatal error in Perl 5.30.
To specify how numbers are formatted when printed, one is adviced
to use printf or sprintf instead.
File::Glob::glob()
will disappearFile::Glob
has a function called glob, which just calls
bsd_glob
. However, its prototype is different from the prototype
of CORE::glob
, and hence, File::Glob::glob
should not
be used.
File::Glob::glob()
was deprecated in Perl 5.8. A deprecation
message was issued from Perl 5.26 onwards, and the function will
disappear in Perl 5.30.
Code using File::Glob::glob()
should call
File::Glob::bsd_glob()
instead.
The simple rule to remember, if you want to match a literal {
character (U+007B LEFT CURLY BRACKET
) in a regular expression
pattern, is to escape each literal instance of it in some way.
Generally easiest is to precede it with a backslash, like \{
or enclose it in square brackets ([{]
). If the pattern
delimiters are also braces, any matching right brace (}) should
also be escaped to avoid confusing the parser, for example,
- qr{abc\{def\}ghi}
Forcing literal { characters to be escaped will enable the Perl
language to be extended in various ways in future releases. To avoid
needlessly breaking existing code, the restriction is is not enforced in
contexts where there are unlikely to ever be extensions that could
conflict with the use there of { as a literal.
Literal uses of { were deprecated in Perl 5.20, and some uses of it
started to give deprecation warnings since. These cases were made fatal
in Perl 5.26. Due to an oversight, not all cases of a use of a literal
{ got a deprecation warning. These cases started warning in Perl 5.26,
and they will be fatal by Perl 5.30.
dump()Use of dump() instead of CORE::dump()
was deprecated in Perl 5.8,
and an unqualified dump() will no longer be available in Perl 5.30.
See dump.
There has been a long-standing bug in Perl that causes a lexical variable not to be cleared at scope exit when its declaration includes a false conditional. Some people have exploited this bug to achieve a kind of static variable. Since we intend to fix this bug, we don't want people relying on this behavior.
Instead, it's recommended one uses state variables to achieve the
same effect:
state variables were introduced in Perl 5.10.
Alternatively, you can achieve a similar static effect by declaring the variable in a separate block outside the function, eg
becomes
The use of my() in a false conditional has been deprecated in
Perl 5.10, and it will become a fatal error in Perl 5.30.
The sysread(), recv(), syswrite() and send() operators are
deprecated on handles that have the :utf8
layer, either explicitly, or
implicitly, eg., with the :encoding(UTF-16LE)
layer.
Both sysread() and recv() currently use only the :utf8
flag for the stream,
ignoring the actual layers. Since sysread() and recv() do no UTF-8
validation they can end up creating invalidly encoded scalars.
Similarly, syswrite() and send() use only the :utf8
flag, otherwise ignoring
any layers. If the flag is set, both write the value UTF-8 encoded, even if
the layer is some different encoding, such as the example above.
Ideally, all of these operators would completely ignore the :utf8
state,
working only with bytes, but this would result in silently breaking existing
code. To avoid this a future version of perl will throw an exception when
any of sysread(), recv(), syswrite() or send() are called on handle with the
:utf8
layer.
In Perl 5.30, it will no longer be possible to use sysread(), recv(), syswrite() or send() to read or send bytes from/to :utf8 handles.
A grapheme is what appears to a native-speaker of a language to be a character. In Unicode (and hence Perl) a grapheme may actually be several adjacent characters that together form a complete grapheme. For example, there can be a base character, like "R" and an accent, like a circumflex "^", that appear when displayed to be a single character with the circumflex hovering over the "R". Perl currently allows things like that circumflex to be delimiters of strings, patterns, etc. When displayed, the circumflex would look like it belongs to the character just to the left of it. In order to move the language to be able to accept graphemes as delimiters, we have to deprecate the use of delimiters which aren't graphemes by themselves. Also, a delimiter must already be assigned (or known to be never going to be assigned) to try to future-proof code, for otherwise code that works today would fail to compile if the currently unassigned delimiter ends up being something that isn't a stand-alone grapheme. Because Unicode is never going to assign non-character code points, nor code points that are above the legal Unicode maximum, those can be delimiters, and their use won't raise this warning.
In Perl 5.30, delimiters which are unassigned code points, or which are non-standalone graphemes will be fatal.
These macros will require an extra parameter in Perl 5.30:
isALPHANUMERIC_utf8
,
isASCII_utf8
,
isBLANK_utf8
,
isCNTRL_utf8
,
isDIGIT_utf8
,
isIDFIRST_utf8
,
isPSXSPC_utf8
,
isSPACE_utf8
,
isVERTWS_utf8
,
isWORDCHAR_utf8
,
isXDIGIT_utf8
,
isALPHANUMERIC_LC_utf8
,
isALPHA_LC_utf8
,
isASCII_LC_utf8
,
isBLANK_LC_utf8
,
isCNTRL_LC_utf8
,
isDIGIT_LC_utf8
,
isGRAPH_LC_utf8
,
isIDCONT_LC_utf8
,
isIDFIRST_LC_utf8
,
isLOWER_LC_utf8
,
isPRINT_LC_utf8
,
isPSXSPC_LC_utf8
,
isPUNCT_LC_utf8
,
isSPACE_LC_utf8
,
isUPPER_LC_utf8
,
isWORDCHAR_LC_utf8
,
isXDIGIT_LC_utf8
,
toFOLD_utf8
,
toLOWER_utf8
,
toTITLE_utf8
,
and
toUPPER_utf8
.
There is now a macro that corresponds to each one of these, simply by
appending _safe
to the name. It takes the extra parameter.
For example, isDIGIT_utf8_safe
corresponds to isDIGIT_utf8
, but
takes the extra parameter, and its use doesn't generate a deprecation
warning. All are documented in Character case changing in perlapi and
Character classification in perlapi.
You can change to use these versions at any time, or, if you can live with the deprecation messages, wait until 5.30 and add the parameter to the existing calls, without changing the names.
The attributes :locked
(on code references) and :unique
(on array, hash and scalar references) have had no effect since
Perl 5.005 and Perl 5.8.8 respectively. Their use has been deprecated
since.
These attributes will no longer be recognized in Perl 5.28, and will then result in a syntax error. Since the attributes do not do anything, removing them from your code fixes the deprecation warning; and removing them will not influence the behaviour of your code.
Perl has allowed you to use a bare here-document terminator to have the here-document end at the first empty line. This practise was deprecated in Perl 5.000, and this will be a fatal error in Perl 5.28.
You are encouraged to use the explictly quoted form if you wish to use an empty line as the terminator of the here-document:
- print <<"";
- Print this line.
- # Previous blank line ends the here-document.
You assigned a reference to a scalar to $/
where the
referenced item is not a positive integer. In older perls this appeared
to work the same as setting it to undef but was in fact internally
different, less efficient and with very bad luck could have resulted in
your file being split by a stringified form of the reference.
In Perl 5.20.0 this was changed so that it would be exactly the same as
setting $/
to undef, with the exception that this warning would be
thrown.
In Perl 5.28, this will throw a fatal error.
You are recommended to change your code to set $/
to undef explicitly
if you wish to slurp the file.
Unicode only allows code points up to 0x10FFFF, but Perl allows much
larger ones. However, using code points exceeding the maximum value
of an integer (IV_MAX
) may break the perl interpreter in some constructs,
including causing it to hang in a few cases. The known problem areas
are in tr///, regular expression pattern matching using quantifiers,
as quote delimiters in qX...X (where X is the chr() of a large
code point), and as the upper limits in loops.
The use of out of range code points was deprecated in Perl 5.24, and it will be a fatal error in Perl 5.28.
If your code is to run on various platforms, keep in mind that the upper limit depends on the platform. It is much larger on 64-bit word sizes than 32-bit ones.
It's allowed to use a list of variables in a format, without separating them with commas. This usage has been deprecated for a long time, and it will be a fatal error in Perl 5.28.
\N{}
Use of \N{}
with nothing between the braces was deprecated in
Perl 5.24, and will throw a fatal error in Perl 5.28.
Since such a construct is equivalent to using an empty string,
you are recommended to remove such \N{}
constructs.
It used to be legal to use open() to associate both a
filehandle and a dirhandle to the same symbol (glob or scalar).
This idiom is likely to be confusing, and it was deprecated in
Perl 5.10.
Using the same symbol to open() a filehandle and a dirhandle
will be a fatal error in Perl 5.28.
You should be using two different symbols instead.
The special variable ${^ENCODING}
was used to implement
the encoding
pragma. Setting this variable to anything other
than undef was deprecated in Perl 5.22. Full deprecation
of the variable happened in Perl 5.25.3.
Setting this variable will become a fatal error in Perl 5.28.
B::OP::terse
This method, which just calls B::Concise::b_terse
, has been
deprecated, and will disappear in Perl 5.28. Please use
B::Concise
instead.
As an (ahem) accidental feature, AUTOLOAD
subroutines are looked
up as methods (using the @ISA
hierarchy) even when the subroutines
to be autoloaded were called as plain functions (e.g. Foo::bar()
),
not as methods (e.g. Foo->bar()
or $obj->bar()
).
This bug will be rectified in future by using method lookup only for
methods' AUTOLOAD
s.
The simple rule is: Inheritance will not work when autoloading
non-methods. The simple fix for old code is: In any module that used
to depend on inheriting AUTOLOAD
for non-methods from a base class
named BaseClass
, execute *AUTOLOAD = \&BaseClass::AUTOLOAD
during
startup.
In code that currently says use AutoLoader; @ISA = qw(AutoLoader);
you should remove AutoLoader from @ISA and change use AutoLoader;
to
use AutoLoader 'AUTOLOAD';
.
This feature was deprecated in Perl 5.004, and will be fatal in Perl 5.28.
The string bitwise operators, &
, |, ^, and ~
, treat
their operands as strings of bytes. As such, values above 0xFF
are nonsensical. Using such code points with these operators
was deprecated in Perl 5.24, and will be fatal in Perl 5.28.
to_utf8_case()
This function is being removed; instead convert to call the appropriate one of: toFOLD_utf8_safe . toLOWER_utf8_safe , toTITLE_utf8_safe , or toUPPER_utf8_safe .
--libpods
in Pod::Html
Since Perl 5.18, the option --libpods
has been deprecated, and
using this option did not do anything other than producing a warning.
The --libpods
option is no longer recognized in Perl 5.26.
c2ph
and pstruct
These old, perl3-era utilities have been deprecated in favour of
h2xs
for a long time. In Perl 5.26, they have been removed.
$SIG {__DIE__}
other than during program exit.The $SIG{__DIE__}
hook is called even inside an eval(). It was
never intended to happen this way, but an implementation glitch made
this possible. This used to be deprecated, as it allowed strange action
at a distance like rewriting a pending exception in $@
. Plans to
rectify this have been scrapped, as users found that rewriting a
pending exception is actually a useful feature, and not a bug.
Perl never issued a deprecation warning for this; the deprecation was by documentation policy only. But this deprecation has been lifted in Perl 5.26.
This message indicates a bug either in the Perl core or in XS
code. Such code was trying to find out if a character, allegedly
stored internally encoded as UTF-8, was of a given type, such as
being punctuation or a digit. But the character was not encoded
in legal UTF-8. The %s
is replaced by a string that can be used
by knowledgeable people to determine what the type being checked
against was.
Passing malformed strings was deprecated in Perl 5.18, and became fatal in Perl 5.26.
*glob{FILEHANDLE}
The use of *glob{FILEHANDLE}
was deprecated in Perl 5.8.
The intention was to use *glob{IO}
instead, for which
*glob{FILEHANDLE}
is an alias.
However, this feature was undeprecated in Perl 5.24.
The following functions in the POSIX
module are no longer available:
isalnum
, isalpha
, iscntrl
, isdigit
, isgraph
, islower
,
isprint
, ispunct
, isspace
, isupper
, and isxdigit
. The
functions are buggy and don't work on UTF-8 encoded strings. See their
entries in POSIX for more information.
The functions were deprecated in Perl 5.20, and removed in Perl 5.24.
It used to be possible to use tie, tied or untie on a scalar
while the scalar holds a typeglob. This caused its filehandle to be
tied. It left no way to tie the scalar itself when it held a typeglob,
and no way to untie a scalar that had had a typeglob assigned to it.
This was deprecated in Perl 5.14, and the bug was fixed in Perl 5.16.
So now tie $scalar
will always tie the scalar, not the handle it holds.
To tie the handle, use tie *$scalar
(with an explicit asterisk). The same
applies to tied *$scalar
and untie *$scalar
.