# Copyright (c) 1997-2005 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.
use vars
qw(@ISA @EXPORT_OK $VERSION);
require List::Util; # List::Util loads the XS
@EXPORT_OK = qw(blessed dualvar reftype weaken isweak tainted readonly openhandle refaddr isvstring looks_like_number set_prototype);
$VERSION = eval $VERSION;
if (grep { /^(weaken|isweak)$/ } @_ ) {
Carp
::croak
("Weak references are not implemented in the version of perl");
if (grep { /^(isvstring)$/ } @_ ) {
Carp
::croak
("Vstrings are not implemented in the version of perl");
if (grep { /^(dualvar|set_prototype)$/ } @_ ) {
Carp
::croak
("$1 is only avaliable with the XS version");
my $rt = reftype
($fh) || '';
return defined(fileno($fh)) ?
$fh : undef
if (reftype
(\
$fh) eq 'GLOB') { # handle openhandle(*DATA)
(tied(*$fh) or defined(fileno($fh)))
eval <<'ESQ' unless defined &dualvar;
use vars qw(@EXPORT_FAIL);
push @EXPORT_FAIL, qw(weaken isweak dualvar isvstring set_prototype);
# The code beyond here is only used if the XS is not installed
# Hope nobody defines a sub by this name
sub UNIVERSAL
::a_sub_not_likely_to_be_here
{ ref($_[0]) }
local($@
, $SIG{__DIE__
}, $SIG{__WARN__
});
?
eval { $_[0]->a_sub_not_likely_to_be_here }
my $pkg = ref($_[0]) or return undef;
bless $_[0], 'Scalar::Util::Fake';
my $i = do { local $^W
; hex $1 };
bless $_[0], $pkg if defined $pkg;
local($@
, $SIG{__DIE__
}, $SIG{__WARN__
});
length($t = ref($r)) or return undef;
# This eval will fail if the reference is not blessed
eval { $r->a_sub_not_likely_to_be_here; 1 }
# we have a GLOB or an IO. Stringify a GLOB gives it's name
$q =~ /^\*/ ?
"GLOB" : "IO";
# OK, if we don't have a GLOB what parts of
# a glob will it populate.
# NOTE: A glob always has a SCALAR
defined *glob{ARRAY
} && "ARRAY"
or defined *glob{HASH
} && "HASH"
or defined *glob{CODE
} && "CODE"
or length(ref(${$r})) ?
"REF" : "SCALAR";
local($@
, $SIG{__DIE__
}, $SIG{__WARN__
});
return 0 if tied($_[0]) || (ref(\
($_[0])) ne "SCALAR");
local($@
, $SIG{__DIE__
}, $SIG{__WARN__
});
!eval { $_[0] = $tmp; 1 };
return 0 if !defined($_) or ref($_);
return 1 if (/^[+-]?\d+$/); # is a +/- integer
return 1 if (/^([+-]?)(?=\d|\.\d)\d*(\.\d*)?([Ee]([+-]?\d+))?$/); # a C float
return 1 if ($] >= 5.008 and /^(Inf(inity)?|NaN)$/i) or ($] >= 5.006001 and /^Inf$/i);
Scalar::Util - A selection of general-utility scalar subroutines
use Scalar::Util qw(blessed dualvar isweak readonly refaddr reftype tainted
weaken isvstring looks_like_number set_prototype);
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
If EXPR evaluates to a blessed reference the name of the package
that it is blessed into is returned. Otherwise C<undef> is returned.
$class = blessed $scalar; # undef
$class = blessed $ref; # undef
$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";
$str = $foo . " world"; # Hello world
If EXPR is a scalar which was coded as a vstring the result is true.
$fmt = isvstring($vs) ? "%vd" : "%s"; #true
If EXPR is a scalar which is a weak reference the result is true.
$weak = isweak($ref); # false
$weak = isweak($ref); # true
B<NOTE>: Copying a weak reference creates a normal, strong, reference.
$weak = isweak($ref); # false
=item looks_like_number EXPR
Returns true if perl thinks EXPR is a number. See
L<perlapi/looks_like_number>.
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
$fh = openhandle("scalar"); # undef
Returns true if SCALAR is readonly.
sub foo { readonly($_[0]) }
$readonly = foo($bar); # false
$readonly = foo(0); # true
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
$addr = refaddr $obj; # eg 88123488
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
$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, '$$';
Return true if the result of EXPR is tainted
$taint = tainted("constant"); # false
$taint = tainted($ENV{PWD}); # true if running under -T
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.
weaken($ref); # Make $ref a weak reference
Note that if you take a copy of a scalar with a weakened reference,
the copy will be a strong reference.
weaken($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
@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
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
Copyright (c) 1997-2005 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.
The weaken and isweak subroutines in this module and the patch to the core Perl
were written in connection with the APress book `Tuomas J. Lukka's Definitive
Guide to Object-Oriented Programming in Perl', to avoid explaining why certain
things would have to be done in cumbersome ways.