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# Scalar::Util.pm # # Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved. # This program is free software; you can redistribute it and/or # modify it under the same terms as Perl itself. package Scalar::Util; use strict; require Exporter; require List::Util; # List::Util loads the XS our @ISA = qw(Exporter); our @EXPORT_OK = qw( blessed dualvar isdual isvstring isweak looks_like_number openhandle readonly refaddr reftype set_prototype tainted weaken ); our $VERSION = "1.27"; $VERSION = eval $VERSION; our @EXPORT_FAIL; unless (defined &weaken) { push @EXPORT_FAIL, qw(weaken); } unless (defined &isweak) { push @EXPORT_FAIL, qw(isweak isvstring); } unless (defined &isvstring) { push @EXPORT_FAIL, qw(isvstring); } sub export_fail { if (grep { /^(?:weaken|isweak)$/ } @_ ) { 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"); } @_; } 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<Scalar::Util> 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<Scalar::Util> does not export any subroutines. The subroutines defined are =over 4 =item blessed EXPR If EXPR evaluates to a blessed reference the name of the package that it is blessed into is returned. Otherwise C<undef> is returned. $scalar = "foo"; $class = blessed $scalar; # undef $ref = []; $class = blessed $ref; # undef $obj = bless [], "Foo"; $class = blessed $obj; # "Foo" =item dualvar NUM, STRING Returns a scalar that has the value NUM in a numeric context and the value STRING in a string context. $foo = dualvar 10, "Hello"; $num = $foo + 2; # 12 $str = $foo . " world"; # Hello world =item isdual EXPR If EXPR is a scalar that is a dualvar, 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 =item isvstring EXPR If EXPR 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); =item looks_like_number EXPR Returns true if perl thinks EXPR is a number. See L<perlapi/looks_like_number>. =item openhandle FH Returns FH if FH may be used as a filehandle and is open, or FH is a tied handle. Otherwise C<undef> is returned. $fh = openhandle(*STDIN); # \*STDIN $fh = openhandle(\*STDIN); # \*STDIN $fh = openhandle(*NOTOPEN); # undef $fh = openhandle("scalar"); # undef =item readonly SCALAR Returns true if SCALAR is readonly. sub foo { readonly($_[0]) } $readonly = foo($bar); # false $readonly = foo(0); # true =item refaddr EXPR If EXPR evaluates to a reference the internal memory address of the referenced value is returned. Otherwise C<undef> is returned. $addr = refaddr "string"; # undef $addr = refaddr \$var; # eg 12345678 $addr = refaddr []; # eg 23456784 $obj = bless {}, "Foo"; $addr = refaddr $obj; # eg 88123488 =item reftype EXPR If EXPR evaluates to a reference the type of the variable referenced is returned. Otherwise C<undef> is returned. $type = reftype "string"; # undef $type = reftype \$var; # SCALAR $type = reftype []; # ARRAY $obj = bless {}, "Foo"; $type = reftype $obj; # HASH =item set_prototype CODEREF, PROTOTYPE Sets the prototype of the given function, or deletes it if PROTOTYPE is undef. Returns the CODEREF. set_prototype \&foo, '$$'; =item tainted EXPR Return true if the result of EXPR is tainted $taint = tainted("constant"); # false $taint = tainted($ENV{PWD}); # true if running under -T =item weaken REF 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, REF will be set to undef. 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<grep()>, 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. =item isweak EXPR If EXPR is a scalar which is a weak reference the result is true. $ref = \$foo; $weak = isweak($ref); # false weaken($ref); $weak = isweak($ref); # true B<NOTE>: Copying a weak reference creates a normal, strong, reference. $copy = $ref; $weak = isweak($copy); # false =back =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 C<isweak> or C<weaken> 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 C<isvstring> you will need to use a newer release of perl. =item C<NAME> is only available with the XS version of Scalar::Util C<Scalar::Util> 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<List::Util> =head1 COPYRIGHT Copyright (c) 1997-2007 Graham Barr <gbarr@pobox.com>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as Perl itself. Except weaken and isweak which are Copyright (c) 1999 Tuomas J. Lukka <lukka@iki.fi>. All rights reserved. This program is free software; you can redistribute it and/or modify it under the same terms as perl itself. =cut