From type/HyperSeq

See Original text in context

multi method serial(HyperSeq:D:)

Converts the object to a Seq and returns it.

From type/RaceSeq

See Original text in context

multi method serial(RaceSeq:D:)

Converts the object to a Seq and returns it.

From type/Any

See Original text in context

multi method serial()

This method is Rakudo specific, and is not included in the Raku spec.

The method returns the self-reference to the instance itself:

my $b;                 # defaults to Any 
say $b.serial.^name;   # OUTPUT: «Any␤» 
say $b.^name;          # OUTPUT: «Any␤» 
my $breakfast = 'food';
$breakfast.serial.say; # OUTPUT: «food␤» 

This is apparently a no-op, as exemplified by the third example above. However, in HyperSeqs and RaceSeqs it returns a serialized Seq, so it can be considered the opposite of the hyper/race methods. As such, it ensures that we are in serial list-processing mode, as opposed to the autothreading mode of those methods.