# Copyright (c) 1997-2007 Graham Barr . All rights reserved. # This program is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. # # Maintained since 2013 by Paul Evans package Scalar::Util; use strict; require Exporter; our @ISA = qw(Exporter); our @EXPORT_OK = qw( blessed refaddr reftype weaken unweaken isweak dualvar isdual isvstring looks_like_number openhandle readonly set_prototype tainted ); our $VERSION = "1.42_02"; $VERSION = eval $VERSION; require List::Util; # List::Util loads the XS List::Util->VERSION( $VERSION ); # Ensure we got the right XS version (RT#100863) our @EXPORT_FAIL; unless (defined &weaken) { push @EXPORT_FAIL, qw(weaken); } unless (defined &isweak) { push @EXPORT_FAIL, qw(isweak isvstring); } unless (defined &isvstring) { push @EXPORT_FAIL, qw(isvstring); } sub export_fail { if (grep { /^(?:weaken|isweak)$/ } @_ ) { require Carp; Carp::croak("Weak references are not implemented in the version of perl"); } if (grep { /^isvstring$/ } @_ ) { require Carp; Carp::croak("Vstrings are not implemented in the version of perl"); } @_; } # set_prototype has been moved to Sub::Util with a different interface sub set_prototype(&$) { my ( $code, $proto ) = @_; return Sub::Util::set_prototype( $proto, $code ); } 1; __END__ =head1 NAME Scalar::Util - A selection of general-utility scalar subroutines =head1 SYNOPSIS use Scalar::Util qw(blessed dualvar isdual readonly refaddr reftype tainted weaken isweak isvstring looks_like_number set_prototype); # and other useful utils appearing below =head1 DESCRIPTION C contains a selection of subroutines that people have expressed would be nice to have in the perl core, but the usage would not really be high enough to warrant the use of a keyword, and the size so small such that being individual extensions would be wasteful. By default C does not export any subroutines. =cut =head1 FUNCTIONS FOR REFERENCES The following functions all perform some useful activity on reference values. =head2 blessed my $pkg = blessed( $ref ); If C<$ref> is a blessed reference the name of the package that it is blessed into is returned. Otherwise C is returned. $scalar = "foo"; $class = blessed $scalar; # undef $ref = []; $class = blessed $ref; # undef $obj = bless [], "Foo"; $class = blessed $obj; # "Foo" Take care when using this function simply as a truth test (such as in C) because the package name C<"0"> is defined yet false. =head2 refaddr my $addr = refaddr( $ref ); If C<$ref> is reference the internal memory address of the referenced value is returned as a plain integer. Otherwise C is returned. $addr = refaddr "string"; # undef $addr = refaddr \$var; # eg 12345678 $addr = refaddr []; # eg 23456784 $obj = bless {}, "Foo"; $addr = refaddr $obj; # eg 88123488 =head2 reftype my $type = reftype( $ref ); If C<$ref> is a reference the basic Perl type of the variable referenced is returned as a plain string (such as C or C). Otherwise C is returned. $type = reftype "string"; # undef $type = reftype \$var; # SCALAR $type = reftype []; # ARRAY $obj = bless {}, "Foo"; $type = reftype $obj; # HASH =head2 weaken weaken( $ref ); The lvalue C<$ref> will be turned into a weak reference. This means that it will not hold a reference count on the object it references. Also when the reference count on that object reaches zero, the reference will be set to undef. This function mutates the lvalue passed as its argument and returns no value. This is useful for keeping copies of references, but you don't want to prevent the object being DESTROY-ed at its usual time. { my $var; $ref = \$var; weaken($ref); # Make $ref a weak reference } # $ref is now undef Note that if you take a copy of a scalar with a weakened reference, the copy will be a strong reference. my $var; my $foo = \$var; weaken($foo); # Make $foo a weak reference my $bar = $foo; # $bar is now a strong reference This may be less obvious in other situations, such as C, for instance when grepping through a list of weakened references to objects that may have been destroyed already: @object = grep { defined } @object; This will indeed remove all references to destroyed objects, but the remaining references to objects will be strong, causing the remaining objects to never be destroyed because there is now always a strong reference to them in the @object array. =head2 unweaken unweaken( $ref ); I The lvalue C will be turned from a weak reference back into a normal (strong) reference again. This function mutates the lvalue passed as its argument and returns no value. This undoes the action performed by L. This function is slightly neater and more convenient than the otherwise-equivalent code my $tmp = $REF; undef $REF; $REF = $tmp; (because in particular, simply assigning a weak reference back to itself does not work to unweaken it; C<$REF = $REF> does not work). =head2 isweak my $weak = isweak( $ref ); Returns true if C<$ref> is a weak reference. $ref = \$foo; $weak = isweak($ref); # false weaken($ref); $weak = isweak($ref); # true B: Copying a weak reference creates a normal, strong, reference. $copy = $ref; $weak = isweak($copy); # false =head1 OTHER FUNCTIONS =head2 dualvar my $var = dualvar( $num, $string ); Returns a scalar that has the value C<$num> in a numeric context and the value C<$string> in a string context. $foo = dualvar 10, "Hello"; $num = $foo + 2; # 12 $str = $foo . " world"; # Hello world =head2 isdual my $dual = isdual( $var ); I If C<$var> is a scalar that has both numeric and string values, the result is true. $foo = dualvar 86, "Nix"; $dual = isdual($foo); # true Note that a scalar can be made to have both string and numeric content through numeric operations: $foo = "10"; $dual = isdual($foo); # false $bar = $foo + 0; $dual = isdual($foo); # true Note that although C<$!> appears to be dual-valued variable, it is actually implemented using a tied scalar: $! = 1; print("$!\n"); # "Operation not permitted" $dual = isdual($!); # false You can capture its numeric and string content using: $err = dualvar $!, $!; $dual = isdual($err); # true =head2 isvstring my $vstring = isvstring( $var ); If C<$var> is a scalar which was coded as a vstring the result is true. $vs = v49.46.48; $fmt = isvstring($vs) ? "%vd" : "%s"; #true printf($fmt,$vs); =head2 looks_like_number my $isnum = looks_like_number( $var ); Returns true if perl thinks C<$var> is a number. See L. =head2 openhandle my $fh = openhandle( $fh ); Returns C<$fh> itself if C<$fh> may be used as a filehandle and is open, or is is a tied handle. Otherwise C is returned. $fh = openhandle(*STDIN); # \*STDIN $fh = openhandle(\*STDIN); # \*STDIN $fh = openhandle(*NOTOPEN); # undef $fh = openhandle("scalar"); # undef =head2 readonly my $ro = readonly( $var ); Returns true if C<$var> is readonly. sub foo { readonly($_[0]) } $readonly = foo($bar); # false $readonly = foo(0); # true =head2 set_prototype my $code = set_prototype( $code, $prototype ); Sets the prototype of the function given by the C<$code> reference, or deletes it if C<$prototype> is C. Returns the C<$code> reference itself. set_prototype \&foo, '$$'; =head2 tainted my $t = tainted( $var ); Return true if C<$var> is tainted. $taint = tainted("constant"); # false $taint = tainted($ENV{PWD}); # true if running under -T =head1 DIAGNOSTICS Module use may give one of the following errors during import. =over =item Weak references are not implemented in the version of perl The version of perl that you are using does not implement weak references, to use L or L you will need to use a newer release of perl. =item Vstrings are not implemented in the version of perl The version of perl that you are using does not implement Vstrings, to use L you will need to use a newer release of perl. =item C is only available with the XS version of Scalar::Util C contains both perl and C implementations of many of its functions so that those without access to a C compiler may still use it. However some of the functions are only available when a C compiler was available to compile the XS version of the extension. At present that list is: weaken, isweak, dualvar, isvstring, set_prototype =back =head1 KNOWN BUGS There is a bug in perl5.6.0 with UV's that are >= 1<<31. This will show up as tests 8 and 9 of dualvar.t failing =head1 SEE ALSO L =head1 COPYRIGHT Copyright (c) 1997-2007 Graham Barr . All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. Additionally L and L which are Copyright (c) 1999 Tuomas J. Lukka . All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as perl itself. Copyright (C) 2004, 2008 Matthijs van Duin. All rights reserved. Copyright (C) 2014 cPanel Inc. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. =cut