sub my_func
{
  my $params = shift;

  print "Message received: " . $params->{message};
  if ($params->{newline}) { print "\n" }
}

# good
my_func( { message => "Hello, world!" } );

# "Error: Not a Hash reference"
my_func( message => "Hello, world!" );

##</code><code>##

sub my_func
{
  my %params;
  if (ref($_[0]) eq 'HASH') {
    %params = %{+shift};
  }
  elsif (ref($_[0]) eq 'ARRAY') {
    (%params) = @{+shift};
  }
  elsif (ref($_[0]) eq 'SCALAR') {
    $params{message} = ${+shift};
  }
  elsif (scalar @_ > 1) {
    (%params) = @_;
  }
  else {
    $params{message} = shift;
  }

  print "Message received: " . $params{message};
  if ($params{newline}) { print "\n" }
}

# good
my_func( { message => "Hello, world!" } );

# also good
my_func( message => "Hello, world!" );