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       Scalar::Util - A selection of general-utility scalar sub-

           use Scalar::Util qw(blessed dualvar isweak readonly refaddr reftype tainted weaken isvstring looks_like_number set_prototype);

       "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 "Scalar::Util" does not export any subroutines.
       The subroutines defined are

       blessed EXPR
           If EXPR evaluates to a blessed reference the name of
           the package that it is blessed into is returned. Oth-
           erwise "undef" is returned.

              $scalar = "foo";
              $class  = blessed $scalar;           # undef

              $ref    = [];
              $class  = blessed $ref;              # undef

              $obj    = bless [], "Foo";
              $class  = blessed $obj;              # "Foo"

       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

       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

       isweak EXPR
           If EXPR is a scalar which is a weak reference the
           result is true.

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               $ref  = \$foo;
               $weak = isweak($ref);               # false
               $weak = isweak($ref);               # true

       looks_like_number EXPR
           Returns true if perl thinks EXPR is a number. See
           "looks_like_number" in perlapi.

       openhandle FH
           Returns FH if FH may be used as a filehandle and is
           open, or FH is a tied handle. Otherwise "undef" is

               $fh = openhandle(*STDIN);           # \*STDIN
               $fh = openhandle(\*STDIN);          # \*STDIN
               $fh = openhandle(*NOTOPEN);         # undef
               $fh = openhandle("scalar");         # undef

       readonly SCALAR
           Returns true if SCALAR is readonly.

               sub foo { readonly($_[0]) }

               $readonly = foo($bar);              # false
               $readonly = foo(0);                 # true

       refaddr EXPR
           If EXPR evaluates to a reference the internal memory
           address of the referenced value is returned. Otherwise
           "undef" is returned.

               $addr = refaddr "string";           # undef
               $addr = refaddr \$var;              # eg 12345678
               $addr = refaddr [];                 # eg 23456784

               $obj  = bless {}, "Foo";
               $addr = refaddr $obj;               # eg 88123488

       reftype EXPR
           If EXPR evaluates to a reference the type of the vari-
           able referenced is returned. Otherwise "undef" is

               $type = reftype "string";           # undef
               $type = reftype \$var;              # SCALAR
               $type = reftype [];                 # ARRAY

               $obj  = bless {}, "Foo";
               $type = reftype $obj;               # HASH

       set_prototype CODEREF, PROTOTYPE
           Sets the prototype of the given function, or deletes
           it if PROTOTYPE is undef. Returns the CODEREF.

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               set_prototype \&foo, '$$';

       tainted EXPR
           Return true if the result of EXPR is tainted

               $taint = tainted("constant");       # false
               $taint = tainted($ENV{PWD});        # true if running under -T

       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

       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) 1997-2004 Graham Barr <gbarrATpobox.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 <lukkaATiki.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

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