I am still learning Perl 6. I am reading the Operators page and I found some unfamiliar constructs at the start of a table:
A Level Examples
N Terms 42 3.14 "eek" qq["foo"] $x :!verbose @$array
I re-read class Array and class Scalar but I am unable to find @$xyz construct in those sections. What do :! and @$ mean? Is there a convenient place that gathers and explains all these symbolic constructs?
@$foo is short for @($foo), where $foo is an item variable and the @(...) syntax simply calls the .list method on its argument. Both the method and the syntactic form are sometimes called the "list/array contextualizer".
One use for it, is when you want to iterate over an Array stored in an item container. An item container is considered a single item by built-ins such as for loops, whereas calling .list on it returns the plain Array without the surrounding item container (i.e. "forces the value to be interpreted in list context"):
my $foo = [1, 2, 3];
say $foo.perl; # $[1, 2, 3]
say $foo.list.perl; # [1, 2, 3]
say @$foo.perl; # [1, 2, 3]
for $foo { ... } # One iteration
for $foo.list { ... } # Three iterations
for @$foo { ... } # Three iterations (identical to the previous line)
:!foo is short for :foo(False), i.e. a named argument that has the value False:
sub do-something (:$verbose = True) { say $verbose; }
do-something; # True
do-something :verbose; # True
do-something :!verbose; # False
When written in term position but not as an argument of an argument list, it constructs a Pair object:
say (:!verbose); # verbose => False