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PERLDEPRECATION(1) Perl Programmers Reference Guide PERLDEPRECATION(1)
NAME
perldeprecation - list Perl deprecations
DESCRIPTION
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.
Perl 5.34
There are no deprecations or fatalizations scheduled for Perl 5.34.
Perl 5.32
Constants from lexical variables potentially modified elsewhere
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":
my $var;
$sub = sub () { return $var };
This usage was deprecated and as of Perl 5.32 is no longer allowed.
Use of strings with code points over 0xFF as arguments to "vec"
"vec" views its string argument as a sequence of bits. A string containing a code point
over 0xFF is nonsensical. This usage is deprecated in Perl 5.28, and was removed in Perl
5.32.
Use of code points over 0xFF in string bitwise operators
The string bitwise operators, "&", "|", "^", and "~", treat their operands as strings of
bytes. As such, values above 0xFF are nonsensical. Some instances of these have been
deprecated since Perl 5.24, and were made fatal in 5.28, but it turns out that in cases
where the wide characters did not affect the end result, no deprecation notice was raised,
and so remain legal. Now, all occurrences either are fatal or raise a deprecation
warning, so that the remaining legal occurrences became fatal in 5.32.
An example of this is
"" & "\x{100}"
The wide character is not used in the "&" operation because the left operand is shorter.
This now throws an exception.
hostname() doesn't accept any arguments
The function "hostname()" in the Sys::Hostname module has always been documented to be
called with no arguments. Historically it has not enforced this, and has actually
accepted and ignored any arguments. As a result, some users have got the mistaken
impression that an argument does something useful. To avoid these bugs, the function is
being made strict. Passing arguments was deprecated in Perl 5.28 and became fatal in Perl
5.32.
Unescaped left braces in regular expressions
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 not enforced in contexts where there are unlikely to ever be extensions
that could conflict with the use there of "{" as a literal. A non-deprecation warning
that the left brace is being taken literally is raised in contexts where there could be
confusion about it.
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. Some cases started
warning in Perl 5.26, and were made fatal in Perl 5.30. Other cases started in Perl 5.28,
and were made fatal in 5.32.
In XS code, use of various macros dealing with UTF-8.
The macros below now require an extra parameter than in versions prior to Perl 5.32. The
final parameter in each one is a pointer into the string supplied by the first parameter
beyond which the input will not be read. This prevents potential reading beyond the end
of the buffer. "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".
Since Perl 5.26, this functionality with the extra parameter has been available by using a
corresponding macro to each one of these, and whose name is formed by appending "_safe" to
the base name. There is no change to the functionality of those. For example,
"isDIGIT_utf8_safe" corresponds to "isDIGIT_utf8", and both now behave identically. All
are documented in "Character case changing" in perlapi and "Character classification" in
perlapi.
This change was originally scheduled for 5.30, but was delayed until 5.32.
"File::Glob::glob()" was removed
"File::Glob" has a function called "glob", which just calls "bsd_glob".
"File::Glob::glob()" was deprecated in Perl 5.8. A deprecation message was issued from
Perl 5.26 onwards, and the function has now disappeared in Perl 5.30.
Code using "File::Glob::glob()" should call "File::Glob::bsd_glob()" instead.
Perl 5.30
$* is no longer supported
Before 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 supported
This 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 advised to use "printf" or
"sprintf" instead.
Assigning non-zero to $[ is fatal
This variable (and the corresponding "array_base" feature and arybase module) allowed
changing the base for array and string indexing operations.
Setting this to a non-zero value has been deprecated since Perl 5.12 and throws a fatal
error as of Perl 5.30.
"File::Glob::glob()" will disappear
"File::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.
Unescaped left braces in regular expressions (for 5.30)
See "Unescaped left braces in regular expressions" above.
Unqualified "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" in perlfunc.
Using my() in false conditional.
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. To allow us to fix this bug,
people should not be relying on this behavior.
Instead, it's recommended one uses "state" variables to achieve the same effect:
use 5.10.0;
sub count {state $counter; return ++ $counter}
say count (); # Prints 1
say count (); # Prints 2
"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, e.g.,
sub f { my $x if 0; return $x++ }
becomes
{ my $x; sub f { return $x++ } }
The use of "my()" in a false conditional has been deprecated in Perl 5.10, and became a
fatal error in Perl 5.30.
Reading/writing bytes from/to :utf8 handles.
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.
Use of unassigned code point or non-standalone grapheme for a delimiter.
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 to be a single character when displayed,
with the circumflex hovering over the "R".
As of Perl 5.30, use of delimiters which are non-standalone graphemes is fatal, in order
to move the language to be able to accept multi-character graphemes as delimiters.
Also, as of Perl 5.30, delimiters which are unassigned code points but that may someday
become assigned are prohibited. 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.
Perl 5.28
Attributes ":locked" and ":unique"
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.
As of Perl 5.28, these attributes are syntax errors. Since the attributes do not do
anything, removing them from your code fixes the syntax error; and removing them will not
influence the behaviour of your code.
Bare here-document terminators
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; as of Perl 5.28,
using a bare here-document terminator throws a fatal error.
You are encouraged to use the explicitly 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.
Setting $/ to a reference to a non-positive integer
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.
As of Perl 5.28, setting $/ to a reference of a non-positive integer throws a fatal error.
You are recommended to change your code to set $/ to "undef" explicitly if you wish to
slurp the file.
Limit on the value of Unicode code points.
Unicode only allows code points up to 0x10FFFF, but Perl allows much larger ones. Up till
Perl 5.28, it was allowed to use code points exceeding the maximum value of an integer
("IV_MAX"). However, that did break the perl interpreter in some constructs, including
causing it to hang in a few cases. The known problem areas were 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; as of Perl 5.28 using a
code point exceeding "IV_MAX" throws a fatal error.
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. For 32-bit
integers, "IV_MAX" equals 0x7FFFFFFF, for 64-bit integers, "IV_MAX" equals
0x7FFFFFFFFFFFFFFF.
Use of comma-less variable list in formats.
It was 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 as of Perl 5.28, this throws a
fatal error.
Use of "\N{}"
Use of "\N{}" with nothing between the braces was deprecated in Perl 5.24, and throws a
fatal error as of Perl 5.28.
Since such a construct is equivalent to using an empty string, you are recommended to
remove such "\N{}" constructs.
Using the same symbol to open a filehandle and a dirhandle
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 throws a fatal error as of
Perl 5.28.
You should be using two different symbols instead.
${^ENCODING} is no longer supported.
The special variable "${^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 to anything other than an undefined value throws a fatal error as of
Perl 5.28.
"B::OP::terse"
This method, which just calls "B::Concise::b_terse", has been deprecated, and disappeared
in Perl 5.28. Please use "B::Concise" instead.
Use of inherited AUTOLOAD for non-method %s::%s() is no longer allowed
As an (ahem) accidental feature, "AUTOLOAD" subroutines were 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 "$obj->bar()").
This bug was deprecated in Perl 5.004, has been rectified in Perl 5.28 by using method
lookup only for methods' "AUTOLOAD"s.
The simple rule is: Inheritance will not work when autoloading non-methods. The simple
fix for old code is: In any module that used to depend on inheriting "AUTOLOAD" for non-
methods from a base class named "BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD"
during startup.
In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);" you should remove
AutoLoader from @ISA and change "use AutoLoader;" to "use AutoLoader 'AUTOLOAD';".
Use of code points over 0xFF in string bitwise operators
The string bitwise operators, "&", "|", "^", and "~", treat their operands as strings of
bytes. As such, values above 0xFF are nonsensical. Using such code points with these
operators was deprecated in Perl 5.24, and is fatal as of Perl 5.28.
In XS code, use of "to_utf8_case()"
This function has been removed as of Perl 5.28; instead convert to call the appropriate
one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe", "toTITLE_utf8_safe", or
"toUPPER_utf8_safe".
Perl 5.26
"--libpods" in "Pod::Html"
Since Perl 5.18, the option "--libpods" has been deprecated, and using this option did not
do anything other than producing a warning.
The "--libpods" option is no longer recognized as of Perl 5.26.
The utilities "c2ph" and "pstruct"
These old, perl3-era utilities have been deprecated in favour of "h2xs" for a long time.
As of Perl 5.26, they have been removed.
Trapping "$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 as of Perl 5.26.
Malformed UTF-8 string in "%s"
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.
Perl 5.24
Use of *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.
Calling POSIX::%s() is deprecated
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.
Perl 5.16
Use of %s on a handle without * is deprecated
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".
SEE ALSO
warnings, diagnostics.
perl v5.34.0 2023-11-23 PERLDEPRECATION(1)
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