in reply to [Perl 6]: Small discoveries V, True / False / FileNotFound

Scalar::Util has dualvar which returns a scalar with both a numeric value and a string value.

In theory, could do:

# untested

sub alsoslick()
{
    if do-stuff
    {
      return dualvar 1, "SomeValue"; # or just a non-0 numeric value
    }
    else
    {
      return dualvar 0, "Some error message";
    }
}

my $result = alsoslick;
if 0+$result
{
    process( '' . $result ); # or just $result if non-error result is 
+numeric
}
else
{
    log-error( '' . $result );
}

[download]

(Not as clean as Perl6.)

Replies are listed 'Best First'.
Re^2: [Perl 6]: Small discoveries V, True / False / FileNotFound
by b2gills (Novice) on Oct 24, 2017 at 23:19 UTC

    Perl 6 also has dual vars

    sub slick()
{
    if do-stuff
    {
      return IntStr.new: 1, "SomeValue";
    }
    else
    {
      return IntStr.new: 0, "Some error message";
    }
}

my $result = slick;
if +$result
{
    process( ~$result );
}
else
{
    log-error( ~$result );
}

    [download]

    I would not do this though, as you can pass around Failures just like any data type which but which act as undefined values.

    sub slick()
{
    if do-stuff
    {
      return "SomeValue";
    }
    else
    {
      fail "Some error message";
    }
}

with slick() # is it defined
-> $result {
  process $result
}
else
-> $error {
  log-error $error.exception.message
}

    [download]

    Actually I would make it so that log-error accepts Failure objects, so that the .exception.message can be removed.

    proto sub log-error ( $ ) {*}
multi sub log-error ( Str $message ) {
  say $message; # do the logging here
}
multi sub log-error ( Exception $exception ) {
  samewith $exception.message
}
multi sub log-error ( Failure $failure ) {
  samewith $failure.exception.message
}

    [download]

    You can also change out any method if you mixin a role.

    # this has the same effect as `but False`
'Some error message' but role { method Bool ( --> False ) {} }

    [download]
[reply]
[d/l]
[select]
      # this has the same effect as `but False`
'Some error message' but role { method Bool ( --> False ) {} }

      [download]
      This is some serious voodoo. No wonder eval is warned of even more.


      holli

      You can lead your users to water, but alas, you cannot drown them.
[reply]
[d/l]

In Section Meditations