Course of Raku / Advanced / Modules / Modules basics

Export tags

Marking a subroutine is export places it in a module’s default export group — the names a plain use brings in. By giving is export a tag, you can sort exports into named groups and let each program pick the set it wants.

A tag is written in parentheses after is export:

unit module Greeting;

sub hello($name)   is export            { "Hello, $name!" }
sub goodbye($name) is export(:partings) { "Goodbye, $name!" }

hello has no tag, so it belongs to the default group; goodbye is tagged :partings.

A plain use imports the default group only:

use Greeting;      # hello is available; goodbye is not

Naming a tag imports that group instead — and, perhaps surprisingly, not the default one as well:

use Greeting :partings; # goodbye is available; hello is not

Asking for :partings gives you exactly that group. To pull in everything a module exports, use the built-in :ALL tag:

use Greeting :ALL; # both hello and goodbye

Two special tags are worth knowing. :ALL is supported by every module and imports all of its exports. :MANDATORY is one you can place on a routine that should be imported no matter which tag the caller chooses.

Each tag is really a package inside the module’s EXPORT package — Greeting::EXPORT::partings, for example — which is exactly what module introspection lists. Tags let a larger module keep its default surface small while still offering extra features on request.

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