Pipe the hash through the call


Use |%hash to pass %hash as named arguments in a sub/method call.

Which, I have to admit, was not a secret.

Fact is that, in Perl, there is no core mechanism to cope with named arguments. Which has always been fine for me, as I happily used hashes (or references thereof) to gain the same effect, assuming the risk of getting keys wrong or coding some form of parameters validation.

On the other hand, in Raku they listened to the needs of the programmers and put a complete and powerful way of managing signatures, including explicit support for named arguments. So this basically work:

sub foo (:$bar) { $bar.put }
foo(bar => 'Hello, World!');

So far so good.

One thing that I did in Perl, though, was collecting arguments for a sub call in a hash, then use the hash as arguments for the call. Something like this:

sub foo { my %args = @_; say $args{bar} }
my %args = (bar => 'Hello, Perl!');

This is not possible in Raku, though, because there is no turning of the hash into a list of arguments and it is passed as a positional argument instead. So this equivalent:

sub foo (:$bar) { $bar.put }
my %hash = (bar => 'Hello, People!');

produces an error:

Too many positionals passed; expected 0 arguments but got 1

The solution? Use a pipe operator |:

sub foo (:$bar) { $bar.put }
my %hash = (bar => 'Hello, Folks!');
# OUTPUT: «Hello, Folks!␤»

From the docs:

Inside argument list Positionals are turned into positional arguments and Associatives are turned into named arguments.

Exactly what I needed, thanks!

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