Packages are nested namespaces of named program elements. Modules, classes, grammars, and others are types of packages. Like files in a directory, you can generally refer to named elements with their short-name if they are local, or with the longer name that includes the namespace to disambiguate as long as their scope allows that.

Names§

A package name is anything that is a legal part of a variable name (not counting the sigil). This includes:

class Foo {
    sub zape () { say "zipi" }
    class Bar {
        method baz () { return 'Þor is mighty' }
        our &zape = { "zipi" };
        our $quux = 42;
    }
}

my $foo;                # simple identifiers
say Foo::Bar.baz;       # calling a method; OUTPUT: «Þor is mighty␤»
say Foo::Bar::zape;     # compound identifiers separated by ::; OUTPUT: «zipi␤»
my $bar = 'Bar';
say $Foo::($bar)::quux; # compound identifiers with interpolations; OUTPUT: «42␤»
$42;                    # numeric names
$!;                     # certain punctuation variables

:: is used to separate nested package names.

Packages do not really have an identity; they can be simply part of a module or class name, for instance. They are more similar to namespaces than to modules. A module of the same name will capture the identity of a package if it exists.

package Foo:ver<0> {};
module Foo:ver<1> {};
say Foo.^ver; # OUTPUT: «1␤»

The syntax allows the declared package to use a version as well as an authority auth, but as a matter of fact, it's dismissed; only modules, classes and other higher order type objects have an identity that might include auth and ver.

package Foo:ver<0>:auth<bar> {};
say Foo.^auth;
# OUTPUT: «(exit code 1) No such method 'auth' for invocant of type
# 'Perl6::Metamodel::PackageHOW' ...

Package-qualified names§

Ordinary package-qualified names look like this: $Foo::Bar::quux, which would be the $quux variable in package Foo::Bar; Foo::Bar::zape would represent the &zape variable in the same package.

Sometimes it's clearer to keep the sigil with the variable name, so an alternate way to write this is:

Foo::Bar::<$quux>

This does not work with the Foo«&zape» variable, since subs, by default, have lexical scope. The name is resolved at compile time because the variable name is a constant. We can access the rest of the variables in Bar (as shown in the example above) since classes, by default, have package scope.

If the name part before :: is null, it means the package is unspecified and must be searched for. Generally this means that an initial :: following the main sigil is a no-op on names that are known at compile time, though ::() can also be used to introduce an interpolation. Also, in the absence of another sigil, :: can serve as its own sigil indicating intentional use of a not-yet-declared package name.

Pseudo-packages§

The following pseudo-package names are reserved at the front of a name:

The following relative names are also reserved but may be used anywhere in a name:

The file's scope is known as UNIT, but there are one or more lexical scopes outside of that corresponding to the linguistic setting (often known as the prelude in other cultures). Hence, the SETTING scope is equivalent to UNIT::OUTERS. For a standard Raku program SETTING is the same as CORE, but various startup options (such as -n or -p) can put you into a domain specific language, in which case CORE remains the scope of the standard language, while SETTING represents the scope defining the DSL that functions as the setting of the current file. When used as a search term in the middle of a name, SETTING includes all its outer scopes up to CORE. To get only the setting's outermost scope, use UNIT::OUTER instead.

Looking up names§

Interpolating into names§

You may interpolate a string into a package or variable name using ::($expr) where you'd ordinarily put a package or variable name. The string is allowed to contain additional instances of ::, which will be interpreted as package nesting. You may only interpolate entire names, since the construct starts with ::, and either ends immediately or is continued with another :: outside the parentheses. Most symbolic references are done with this notation:

my $foo = "Foo";
my $bar = "Bar";
my $foobar = "Foo::Bar";
$::($bar)              # lexically-scoped $Bar
$::("MY::$bar")        # lexically-scoped $Bar
$::("OUR::$bar")       # package-scoped $Bar
$::("GLOBAL::$bar")    # global $Bar
$::("PROCESS::$bar")   # process $Bar
$::("PARENT::$bar")    # current package's parent's $Bar
$::($foobar)           # $Foo::Bar
@::($foobar)::baz      # @Foo::Bar::baz
@::($foo)::Bar::baz    # @Foo::Bar::baz
@::($foobar)baz        # ILLEGAL at compile time (no operator baz)
@::($foo)::($bar)::baz # @Foo::Bar::baz

An initial :: doesn't imply global; here as part of the interpolation syntax it doesn't even imply package. After the interpolation of the ::() component, the indirect name is looked up exactly as if it had been there in the original source code, with priority given first to leading pseudo-package names, then to names in the lexical scope (searching scopes outwards, ending at CORE). The current package is searched last.

Use the MY pseudopackage to limit the lookup to the current lexical scope, and OUR to limit the scopes to the current package scope.

In the same vein, class and method names can be interpolated too:

role with-method {
    method a-method { return 'in-a-method of ' ~ $?CLASS.^name  };
}

class a-class does with-method {
    method another-method { return 'in-another-method' };
}

class b-class does with-method {};

my $what-class = 'a-class';

say ::($what-class).a-method; # OUTPUT: «in-a-method of a-class␤»
$what-class = 'b-class';
say ::($what-class).a-method; # OUTPUT: «in-a-method of b-class␤»

my $what-method = 'a-method';
say a-class."$what-method"(); # OUTPUT: «in-a-method of a-class␤»
$what-method = 'another-method';
say a-class."$what-method"(); # OUTPUT: «in-another-method␤»

Direct lookup§

To do direct lookup in a package's symbol table without scanning, treat the package name as a hash:

Foo::Bar::{'&baz'}  # same as &Foo::Bar::baz
PROCESS::<$IN>      # same as $*IN
Foo::<::Bar><::Baz> # same as Foo::Bar::Baz

Unlike ::() symbolic references, this does not parse the argument for ::, nor does it initiate a namespace scan from that initial point. In addition, for constant subscripts, it is guaranteed to resolve the symbol at compile time.

You cannot use this kind of direct lookup inside regular expressions, unless you issue a MONKEY-SEE-NO-EVAL pragma. The main intention of this measure is to avoid user input being executed externally.

The null pseudo-package is the same search list as an ordinary name search. That is, the following are all identical in meaning:

$foo
::{'$foo'}
::<$foo>

Each of them scans the lexical scopes outward, and then the current package scope (though the package scope is then disallowed when `use strict` is in effect).

Package lookup§

Subscript the package object itself as a hash object, the key of which is the variable name, including any sigil. The package object can be derived from a type name by use of the :: postfix:

MyType::<$foo>

Class member lookup§

Methods—including auto-generated methods, such as public attributes' accessors—are stored in the class metaobject and can be looked up through by the lookup method.

Str.^lookup('chars')

Globals§

Interpreter globals live in the GLOBAL package. The user's program starts in the GLOBAL package, so "our" declarations in the mainline code go into that package by default. Process-wide variables live in the PROCESS package. Most predefined globals such as $*UID and $*PID are actually process globals.

Programmatic use of modules§

It is sometimes useful to be able to programmatically define and use modules. Here is a practical example.

Assume we have a series of modules with the module files in a directory tree like this:

lib/
    TomtomMaps/
        Example/
            # a directory of example file modules programmatically
            # created from the Tomtom Maps SDK
            A01.rakumod
            #...
            C09.rakumod
            #...

Module TomtomMaps::Example::C09 looks like this:

unit module TomtomMaps::Example::C09;

# ensure you use the 'our' declarator
our sub print-example($fh, # filehandle open for writing
                      :$api-maps-key
) { # do not need to export the sub
    $fh.print: qq:to/HERE/;
    # ... the example html file
    HERE
}

We can access and use the subroutines like this:

use lib 'lib';
my $module-dir = 'TomtomMaps::Example';
my $example    = 'C09';
my $m          = "{$module-dir}::{$example}";

# you must use the runtime 'require', not the compile-time 'use'
require ::($m);

my $fh = open "./example-{$example}.html", :w;
my $api-maps-key = 'ghghfxnnhrgfsWE.mmn';

# execute the subroutine
&::($m)::print-example($fh, :$api-maps-key); # the map's html file is written

$fh.close;