Ubuntu Manpage: perldeprecation - list Perl deprecations

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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".

NAME

DESCRIPTION

SEE ALSO