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Scalar::Util zef:lizmat last updated on 2021-09-09


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Raku port of Perl's Scalar::Util module 1.55


use Scalar::Util <blessed dualvar isdual readonly refaddr reftype
                  isvstring looks_like_number openhandle>


This module tries to mimic the behaviour of Perl's Scalar::Util module as closely as possible in the Raku Programming Language.

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 would be so small that being individual extensions would be wasteful.

By default Scalar::Util does not export any subroutines.


my $class = blessed( $object );

Returns the name of the class of the object.


my $addr = refaddr( $object );

Returns the internal memory address of the object as a plain integer. Please note that Raku implementations do not require the memory address of an object to be constant: in fact, with MoarVM as a back end, any longer living object will have its memory address changed over its lifetime.


my $type = reftype( $object );

For objects performing the Positional role, ARRAY will be returned. For objects performing the Associative role, HASH will be returned. Otherwise Nil will be returned.


my $var = dualvar( $num, $string );

Returns a scalar that has the value $num when used as a number and the value $string when used as a string.

$foo = dualvar 10, "Hello";
$num = $foo + 2;                    # 12
$str = $foo . " world";             # Hello world


my $dual = isdual( $var );

If $var is a scalar that has both numeric and string values, the result is true.

$foo = dualvar 86, "Nix";
$dual = isdual($foo);               # True


my $vstring = isvstring( $var );

Returns whether $var is a Version object.

$vs    = v49.46.48;
$isver = isvstring($vs);            # True


my $isnum = looks_like_number( $var );

Returns true if $var can be coerced to a number.


my $ro = readonly( $var );

Returns true if $var is readonly (aka does not have a container).

sub foo(\value) { readonly(value) }

$readonly = foo($bar);              # False
$readonly = foo(0);                 # True


my $fh = openhandle( $fh );

Returns $fh itself if $fh may be used as a filehandle and is open, or is
is a tied handle. Otherwise <Nil> is returned.

    $fh = openhandle($*STDIN);
    $fh = openhandle($notopen);         # Nil
    $fh = openhandle("scalar");         # Nil


It did not make sense to port the following functions to Raku, as they pertain to specific Pumpkin Perl internals.

weaken isweak unweaken set_prototype tainted

Attempting to import these functions will result in a compilation error with hopefully targeted feedback. Attempt to call these functions using the fully qualified name (e.g. Scalar::Util::weaken($a)) will result in a run time error with the same feedback.




Elizabeth Mattijsen [email protected]

Source can be located at: . Comments and Pull Requests are welcome.


Copyright 2018, 2019, 2020, 2021 Elizabeth Mattijsen

This library is free software; you can redistribute it and/or modify it under the Artistic License 2.0.

Re-imagined from the Perl version as part of the CPAN Butterfly Plan. Perl version originally developed by Graham Barr, subsequently maintained by Matthijs van Duin, cPanel and Paul Evans.