Vimwiki::Files Module

A module I'm currently writing for analyzing a markdown file to help me process their conversion to HTML for output to this website. I want this module to be a subclass of IO::Path so it inherits its methods.

Subclassing IO::Path


  • I ran into problems right away trying to subclass Raku's IO::Path module
  • Looked for help from community

Help from Stackoverflow

  • Posted question to stackoverflow about it
    • raku - How to make a class that inherits the same methods as IO::Path? - Stack Overflow:
    • recevied an answer
      • from user "raiph"
      • gave me tips for subclassing IO::Path
        • create a new method in child class
        • use nextwith function call in new method
      • at first the answer seemed to work
        • quickly ran into problems, however
          • I was unable to manipulate attributes of my subclass
            • unable to get my object to set/use its own attributes
    • raiph then modified his original answer later
      • suggested that the $.path attribute I had in the child class was a problem
        • would conflict with original IO::Path module
      • raiph now recommended delegating IO::Path methods through an attribute

The Struggle Continues

  • I was still curious about how to subclass IO::Path
    • wanted to learn
    • partially took raiph's recommendation and tried to get subclassing working
      • removed the $!path attribute
      • still ran into a bunch of problems
  • spent hours trying to get it to work but was unable to
    • The good news is I learned some stuff in the process
      • One module I found extends IO::Path
        • IO::Path::More
        • Uses augment
          • not recommended to use
          • can't add your own attributes to the child class when using augment

Help from IRC

  • started to feel dumb, dejected and defeated :)
  • finally gave in and posted code IRC to see if anyone could help me figure this out
    • posted my last best attempt to get it working:
        #! /usr/bin/env raku
        use v6;
        class Vimwiki::File is IO::Path {
            has $.blah;
            multi method new($path) {
            submethod BUILD() {
                say 'hi';
                $!blah = 'test';
                say $!blah;
        my $vwf ='t/');
        say $vwf.^mro;
        say $vwf.s;
        say $vwf.blah;
    • the code outputs:
            ((File) (Path) (Cool) (Any) (Mu))
    • I asked why was say $vwf.blah not returning any results?
    • went to bed, waited for Europeans to wake up
      • where are the American Raku developers, btw?

Upshot: IO::Path may not be subclassifiable

Solution! Thanks raiph

  • Finally got around to raiph's suggestion to delegate. This seems to work perfectly:
    unit class Vimwiki::File;

    has IO::Path $.path is required handles * where *.IO.e;
    has $.content;

    multi method new($path) {
        self.bless(path => IO::Path($path));

    submethod TWEAK() {
        $!content = $!path.slurp;
  • Just not sure if I'm using TWEAK right or not
    • I thought TWEAK took same arguments as new constructor
      • I don't appear to need any arguments, though

What did we learn?

  • Raku is still a little rough around the edges
    • Probably somewhat expected
      • It's fairly new
      • It's a huge, complex language
  • if you're a beginner
    • You can kill a lot of time banging your head on a problem
    • probably best to go with what works immedately and move on
      • on the other hand
        • my diligence brought attention to a problem
        • while frustrating, you can learn a lot during the process
  • if you're much more skilled
    • Raku is an opportunity to build upon a great foundation and pick up skill building the language

One more thing

unit class Vimwiki::File is IO::Path;
    has $.content;
    method !SET-SELF() {
        $!content = self.slurp;

    method new($path) {
        $path.IO.e ?? self.IO::Path::new($path)!SET-SELF() 
                  !! die "$path is not a file";
  • The TWEAK and BUILD methods are still ignored
    • the SET-SELF method takes care of that
      • is a private method, hence the ! before the name
Last updated: March 6, 2022 2:28 AM
First published: January 31, 2022