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P5ref zef:lizmat last updated on 2021-09-09

lib/P5ref.rakumod
use v6.d;

unit module P5ref:ver<0.0.7>:auth<zef:lizmat>;

proto sub ref(|) is export {*}
multi sub ref() { ref CALLERS::<$_> }
multi sub ref(\this) {
    my \what = this<>.WHAT;         # decontainerize
    what =:= Array
      ?? 'ARRAY'
      !! what =:= Hash
        ?? 'HASH'
        !! what =:= Regex
          ?? 'Regexp'
          !! what ~~ Callable       # don't expect to be subclassing Callable
            ?? 'CODE'
            !! what =:= Version
              ?? 'VSTRING'
              !! this.VAR.^name eq 'Proxy'
                ?? 'SCALAR'
                !! this.^name         # whatever else
}

=begin pod

=head1 NAME

Raku port of Perl's ref() built-in

=head1 SYNOPSIS

  use P5ref; # exports ref()

  my @a;
  say ref @a;  # ARRAY

  my %h;
  say ref %h;  # HASH

  sub &a { };
  say ref &a;  # CODE

  my $r = /foo/;
  say ref $r;  # Regexp

  my $v = v6.c;
  say ref $v;  # VSTRING

  my $i = 42;
  say ref $i;  # Int

=head1 DESCRIPTION

This module tries to mimic the behaviour of Perl's C<ref> built-in as
closely as possible in the Raku Programming Language.

=HEAD1 ORIGINAL PERL 5 DOCUMENTATION

    ref EXPR
    ref     Returns a non-empty string if EXPR is a reference, the empty
            string otherwise. If EXPR is not specified, $_ will be used. The
            value returned depends on the type of thing the reference is a
            reference to.

            Builtin types include:

                SCALAR
                ARRAY
                HASH
                CODE
                REF
                GLOB
                LVALUE
                FORMAT
                IO
                VSTRING
                Regexp

            You can think of "ref" as a "typeof" operator.

                if (ref($r) eq "HASH") {
                    print "r is a reference to a hash.\n";
                }
                unless (ref($r)) {
                    print "r is not a reference at all.\n";
                }

            The return value "LVALUE" indicates a reference to an lvalue that
            is not a variable. You get this from taking the reference of
            function calls like "pos()" or "substr()". "VSTRING" is returned
            if the reference points to a version string.

            The result "Regexp" indicates that the argument is a regular
            expression resulting from "qr//".

            If the referenced object has been blessed into a package, then
            that package name is returned instead. But don't use that, as it's
            now considered "bad practice". For one reason, an object could be
            using a class called "Regexp" or "IO", or even "HASH". Also, "ref"
            doesn't take into account subclasses, like "isa" does.

            Instead, use "blessed" (in the Scalar::Util module) for boolean
            checks, "isa" for specific class checks and "reftype" (also from
            Scalar::Util) for type checks. (See perlobj for details and a
            "blessed/isa" example.)

            See also perlref.

=head1 PORTING CAVEATS

=head2 Types not supported

The following strings are currently never returned by C<ref> because they have
no sensible equivalent in Raku: C<REF>, C<GLOB>, C<LVALUE>, C<FORMAT>, C<IO>.

Also, since everything in Raku is a (blessed) object, you can only get the
C<SCALAR> response if you managed to put a Scalar container into another
Scalar container (which is pretty hard), or you somehow have gotten ahold of
a Proxy object.  On all other cases, a Scalar container will be ignored and
instead the contents of the container will be used.

=head2 $_ no longer accessible from caller's scope

In future language versions of Raku, it will become impossible to access the
C<$_> variable of the caller's scope, because it will not have been marked as
a dynamic variable.  So please consider changing:

    ref;

to either:

    ref($_);

or, using the subroutine as a method syntax, with the prefix C<.> shortcut
to use that scope's C<$_> as the invocant:

    .&ref;

=head1 AUTHOR

Elizabeth Mattijsen <[email protected]>

Source can be located at: https://github.com/lizmat/P5ref . Comments and
Pull Requests are welcome.

=head1 COPYRIGHT AND LICENSE

Copyright 2018, 2019, 2020, 2021 Elizabeth Mattijsen

Re-imagined from Perl as part of the CPAN Butterfly Plan.

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

=end pod

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