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 5.32
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 has been deprecated, and will no longer be allowed in Perl
5.32.
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 adviced to
use "printf" or "sprintf" instead.
"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
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.
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. 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:
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, eg
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 it will become 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 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.
In XS code, use of various macros dealing with UTF-8.
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.
Perl 5.28
Attribute "%s" is deprecated, and will disappear in 5.28
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.
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, 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.
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.
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.
Limit on the value of Unicode code points.
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.
Use of comma-less variable list in formats.
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.
Use of "\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.
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 will be
a fatal error in 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 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.
Use of inherited AUTOLOAD for non-method %s() is deprecated
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 "$obj->bar()").
This bug will be rectified in future by using method lookup only for
methods' "AUTOLOAD"s.
The simple rule is: Inheritance will not work when autoloading non-
methods. The simple fix for old code is: In any module that used to
depend on inheriting "AUTOLOAD" for non-methods from a base class named
"BaseClass", execute "*AUTOLOAD = \&BaseClass::AUTOLOAD" during
startup.
In code that currently says "use AutoLoader; @ISA = qw(AutoLoader);"
you should remove AutoLoader from @ISA and change "use AutoLoader;" to
"use AutoLoader 'AUTOLOAD';".
This feature was deprecated in Perl 5.004, and will be fatal in Perl
5.28.
Use of code points over 0xFF in string bitwise operators
The string bitwise operators, "&", "|", "^", and "~", treat their
operands as strings of bytes. As such, values above 0xFF are
nonsensical. Using such code points with these operators was deprecated
in Perl 5.24, and will be fatal in Perl 5.28.
In XS code, use of "to_utf8_case()"
This function is being removed; instead convert to call the appropriate
one of: "toFOLD_utf8_safe". "toLOWER_utf8_safe", "toTITLE_utf8_safe",
or "toUPPER_utf8_safe".
Perl 5.26
"--libpods" in "Pod::Html"
Since Perl 5.18, the option "--libpods" has been deprecated, and using
this option did not do anything other than producing a warning.
The "--libpods" option is no longer recognized in Perl 5.26.
The utilities "c2ph" and "pstruct"
These old, perl3-era utilities have been deprecated in favour of "h2xs"
for a long time. In Perl 5.26, they have been removed.
Trapping "$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 in
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 v5.26.3 2018-03-23 PERLDEPRECATION(1)
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