PositionalBindFailover Reference

Failover for binding to a Positional

What it is #

Position in the hierarchy #

Routines #

Signatures are reproduced from the documentation, including their declared return types. A routine listed here is part of the type's published interface; whether Raku++ implements it is a separate question, answered by the examples below.

method cache #

method cache(PositionalBindFailover:D: --> List:D)

Returns List:D.

Returns a List based on the iterator method, and caches it. Subsequent calls to cache always return the same List object.

method list #

multi method list(::?CLASS:D:)

Returns a List based on the iterator method without caching it.

method iterator #

method iterator(PositionalBindFailover:D:) { ... }

This method stub ensure that a class implementing role PositionalBindFailover provides an iterator method.

Examples, run three ways #

Every example below comes from the official documentation, together with the output that documentation asserts. Each was then executed by Rakudo and by Raku++ when this page was built. Where the three agree, one result is shown; where they do not, all three are — because which of them is wrong is exactly the information worth having.

2 no-output · 1 not-runnable · 1 ok

role PositionalBindFailover { ... }

sub fifths(@a) {        # @a is constraint to Positional
    @a[4];
}
my $seq := gather {     # a Seq, which is not Positional
    take $_ for 1..*;
}
say fifths($seq);       # OUTPUT: «5␤»

5

class Foo does PositionalBindFailover {
    method iterator {
        class :: does Iterator {
            method pull-one {
                return 42 unless $++;
                IterationEnd
            }
        }.new
    }
}

sub first-five (@a) { @a[^5].say }
first-five Foo.new; # OUTPUT: # OUTPUT: «(42 Nil Nil Nil Nil)␤»