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P5fileno zef:lizmat last updated on 2021-09-09

lib/P5fileno.rakumod
use v6.*;

unit module P5fileno:ver<0.0.6>:auth<zef:lizmat>;

proto sub fileno(|) is export {*}
multi sub fileno(IO::Handle:D $handle --> Int:D) {
    if $handle.opened {
        my $fileno;
        CATCH { default { $fileno = -1 } }
        $fileno = $handle.native-descriptor;
    }
    else {
        Nil
    }
}

=begin pod

=head1 NAME

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

=head1 SYNOPSIS

  use P5fileno;

  say fileno $*IN;    # 0
  say fileno $*OUT;   # 1
  say fileno $*ERR;   # 2
  say fileno $foo;    # something like 16

=head1 DESCRIPTION

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

=head1 ORIGINAL PERL 5 DOCUMENTATION

    fileno FILEHANDLE
            Returns the file descriptor for a filehandle, or undefined if the
            filehandle is not open. If there is no real file descriptor at the
            OS level, as can happen with filehandles connected to memory
            objects via "open" with a reference for the third argument, -1 is
            returned.

            This is mainly useful for constructing bitmaps for "select" and
            low-level POSIX tty-handling operations. If FILEHANDLE is an
            expression, the value is taken as an indirect filehandle,
            generally its name.

            You can use this to find out whether two handles refer to the same
            underlying descriptor:

                if (fileno(THIS) != -1 && fileno(THIS) == fileno(THAT)) {
                    print "THIS and THAT are dups\n";
                } elsif (fileno(THIS) != -1 && fileno(THAT) != -1) {
                    print "THIS and THAT have different " .
                        "underlying file descriptors\n";
                } else {
                    print "At least one of THIS and THAT does " .
                        "not have a real file descriptor\n";
                }

=head1 IDIOMATIC PERL 6 WAY

The file descriptor of a file handle is exposed with the C<native-descriptor>
method on C<IO::Handle>:

    say $*OUT.native-descriptor;   # 1

=head1 PORTING CAVEATS

When calling with an unopened C<IO::Handle>, this version will return C<Nil>.
That's the closest thing there is to C<undef> in Raku.

=head1 AUTHOR

Elizabeth Mattijsen <[email protected]>

Source can be located at: https://github.com/lizmat/P5fileno . 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

# vim: expandtab shiftwidth=4