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.
Unscheduled Deprecations
Unicode Delimiter Will be Paired
Some unicode delimiters used to be allowed as single characters, but in
the future will be part of a balanced pair. This deprecation category is
used to mark the ones that will change from being unpaired to paired.
Category: "deprecated::delimiter_will_be_paired"
Dot In Inc
The current working directory "." used to be automatically included in
@INC, but in Perl 5.26 this was removed for security reasons. Ever since
then we have produced a warning when a user uses "do EXPR" and "EXPR"
does not include a path, and the file was not found in any directory in
@INC but was located in ".". The file will not be loaded but a
deprecated warning will be generated.
Category: "deprecated::dot_in_inc"
Unicode Property Name
Various types of unicode property name will generate deprecated warnings
when used in a regex pattern. For instance surrogate characters will
result in deprecation warnings.
Category: "deprecated::unicode_property_name"
Perl 5.44
Calling a missing import() or unimport() method with an argument
Historically calling import() or unimport() on any class which did not
define such a method would be silently ignored. Effectively Perl behaved
as though there was an empty method defined in the "UNIVERSAL" package
(even when there was no such method actually defined). As of Perl
version 5.39.2 calling such a method with an argument will trigger a
warning, and in Perl version 5.44 this warning will be upgraded to an
error. (Calling such a method with no arguments at all will always be
safe.)
Category: "deprecated::missing_import_called_with_args"
Changing "use VERSION" while another "use VERSION" is in scope
A "use VERSION" declaration has many implicit effects on the surrounding
scope, such as strict and feature flags, or importing builtin functions.
Once you have a "use VERSION" statement in scope, another "use VERSION"
statement with a different version is now deprecated since Perl 5.39.8,
due to the increasing complexity of swapping from one prevailing version
to another.
Category: "deprecated::subsequent_use_version"
Perl 5.42
Smartmatch
Smartmatch is now seen as a failed experiment and was marked as
deprecated in Perl 5.37.10. This includes the "when" and "given"
keywords, as well as the smartmatch operator "~~". The feature will be
removed entirely in the Perl 5.42.0 production release.
Category: "deprecated::smartmatch"
Goto Block Construct
"goto LABEL;" will produce a deprecated warning when jumping into the
body of a loop or other block construct from outside. For instance
while (should_loop($x)) {
LABEL:
do_stuff();
}
goto LABEL;
will produce a warning that this behavior is deprecated. In general you
should just avoid doing this; the people that maintain your code will be
grateful for your restraint.
Category: "deprecated::goto_construct"
Use of "'" as a global name separator
Perl allows use of "'" instead of "::" to replace the parts of a package
or global variable name, for example "A::B" and "A'B" are equivalent.
"'" will no longer be recognized as a name separator in Perl 5.42.
Category: "deprecated::apostrophe_as_package_separator"
Perl 5.40
Downgrading a "use VERSION" to below v5.11
Once Perl has seen a "use VERSION" declaration that requests a version
"v5.11" or above, a subsequent second declaration that requests an
earlier version will print a deprecation warning. For example,
use v5.14;
say "We can use v5.14's features here";
use v5.10; # This prints a warning
This was deprecated in Perl 5.36 and is now fatal.
This is because of an intended related change to the interaction between
"use VERSION" and "use strict". If you specify a version >= 5.11, strict
is enabled implicitly. If you request a version < 5.11, strict will
become disabled even if you had previously written "use strict". This
was not the previous behaviour of "use VERSION", which at present will
track explicitly-enabled strictness flags independently.
Category: "deprecated::version_downgrade"
Perl 5.38
Pod::Html utility functions
The definition and documentation of three utility functions previously
importable from Pod::Html were moved to new package Pod::Html::Util in
Perl 5.36. While they remained importable from Pod::Html in Perl 5.36,
as of Perl 5.38 they are only importable, on request, from
Pod::Html::Util.
Perl 5.34
There were no deprecations or fatalizations in 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 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 compared to 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" had a function called "glob", which just called "bsd_glob".
File::Glob::glob() was deprecated in Perl 5.8. A deprecation message was
issued from Perl 5.26 onwards, the function became fatal in Perl 5.30,
and was removed entirely in Perl 5.32.
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 relic from the past lost its special
meaning in 5.10. Use of this variable became 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
basis, 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 became 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.
Unqualified dump()
Use of dump() instead of CORE::dump() was deprecated in Perl 5.8, and an
unqualified dump() is no longer available as of 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
UTF-16LE 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 handles with the ":utf8" layer.
As of Perl 5.30, it is no longer 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 to 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 and 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';".
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.
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