Scalar::Util(3pm) - phpMan

Scalar::Util(3)       User Contributed Perl Documentation      Scalar::Util(3)

NAME
       Scalar::Util - A selection of general-utility scalar subroutines
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
DESCRIPTION
       "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. Otherwise "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
       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 $! 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
       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);
       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 returned.
               $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 variable
           referenced is returned. Otherwise "undef" is returned.
               $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.
               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
           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 "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.
       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
           NOTE: Copying a weak reference creates a normal, strong, reference.
               $copy = $ref;
               $weak = isweak($copy);              # false
DIAGNOSTICS
       Module use may give one of the following errors during import.
       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 "isweak" or "weaken" you will need to use a
           newer release of perl.
       Vstrings are not implemented in the version of perl
           The version of perl that you are using does not implement Vstrings,
           to use "isvstring" you will need to use a newer release of perl.
       "NAME" is only available with the XS version of Scalar::Util
           "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
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
SEE ALSO
       List::Util
COPYRIGHT
       Copyright (c) 1997-2007 Graham Barr <gbarr AT 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 AT 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.

perl v5.16.3                      2012-12-27                   Scalar::Util(3)