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Quickly: Using a sub as a method

| 187 words | 1 minutes | raku quickly
Docked submarine

Quickly now, let’s consider the difference between a sub and a method. When programming Perl 6, the only significant difference between a sub and a method is that a method always takes at least one positional argument whereas a sub only takes what’s listed in the parameter list. In a method, the required first positional parameter is not passed as part of the parameter list, but assigned to self.

For example,

class Demo {
    has $.value;
    sub foo(Demo $val) is export { put $val }
    method bar() { put self }
    method Str() { ~$.value }

import Demo;

my $demo = => 42);
foo($demo);  # OUTPUT: «42»
$; # OUTPUT: «42»

Ready for the trick? The subroutine can be called as a method too, like this:

$demo.&foo; # OUTPUT: «42»

That’s it. Any subroutine can be used as a method by using the .& operator to make the call. The object before the operation will be passed as the first argument.

My favorite usage of this feature is this one:

use JSON::Fast;
my %data = "config.json".IO.slurp.&from-json;

There’s more, but I’m just posting this quickly.


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