Anonmonk, here is how but I can't see how this is related to Inline::C.

Case2 (pass a scalar - not a ref) is obviously failing. But I don't think that should apply to Inline::C because AFAICT a scalar, like a scalarref and any ref, is passed as an SV * which I can affect its PV field within func() and insert an arrayref in there. A good warmup though thanks.

use strict;
use warnings;

use Test::More;

use Data::Dumper;

my $correct_result = make_a_rowsxcols_array(5,3);
print Dumper($correct_result);

### $#out = -1; # clears an array;

# Case1: pass it an arrayref
my $T = 'Case1';
my @out = (1,2,3);
is( case1(\@out), 0, "$T: returned success.");
is_deeply(\@out, $correct_result, "$T: correct result.");

# Case2: pass it a scalar
$T = 'Case2';
my $x = 123;
is( case2($x), 0, "$T: returned success.");
is_deeply($x, $correct_result, "$T: correct result.");

# Case3: pass it a scalarref
$T = 'Case3';
my $y = 123;
is( case3(\$y), 0, "$T: returned success.");
is_deeply($y, $correct_result, "$T: correct result.");

done_testing();

sub case1 {
    # pass an arrayref, clear it and make it 5rowsx3cols
    my $out = $_[0];
    return 1 unless ref($out) eq 'ARRAY';
    $#{ $out } = -1;
    push @$out, @{ make_a_rowsxcols_array(5,3) };
    return 0;
}

sub case2 {
    # pass a simple scalar, make it an arrayref
    my $out = $_[0];
    return 1 unless ref($out) eq '';

    $out = make_a_rowsxcols_array(5,3);
    return 0;
}

sub case3 {
    # pass a scalarref, fill it with an arrayref to 5rowsx3cols
    my $out = $_[0];
    return 1 unless ref($out) eq 'SCALAR';

    undef $$out;
    $$out = make_a_rowsxcols_array(5,3);
    return 0;
}


sub make_a_rowsxcols_array {
    [ map { [ (42)x$_[1] ] } 1..$_[0] ]
}
[download]

bw, bliako