What does the plus in the method declaration in perl6 mean?

Question

What does plus mean in method declarations in Perl6?

Here is an example from spec

submethod BUILD (+$tail, +@legs , *%extraargs) { $.tail = $tail; @:legs = @legs; } 

Answer 1

About a week ago (September 2015), Larry Wall introduced the new + prefix, one of four parameter prefixes ( * , ** , + , | ), which mean sloppy (variable) parameters . So far, he has added this new prefix to the Rakudo Perl 6 compiler, added several tests, given a brief unofficial description of it in # perl6, and added a section on it to the corresponding language document.

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The example given in the original question is taken from the archive of an unofficial document written and frozen in time ten years ago. At that time, the + parameter prefix meant a named parameter, as opposed to a positional one . Currently we use for this : thus:

 submethod BUILD (:$tail, :@legs, *%extraargs) { $.tail = $tail; @.legs = @legs; } 

Answer 2

Your "spec" references are related to a historical document, and the syntax has long gone with Perl 6. I'm not sure if it used perhaps "at least one argument", similar to the + quantifier in regular expressions.

For the latest specs, please read the http://perlcabal.org/syn/S06.html , which contains all the information about signatures and routines.