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

Problem

• 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: stackoverflow.com
  • 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($path) {
              self.bless;
              nextwith($path);
          }
  
          submethod BUILD() {
              say 'hi';
              $!blah = 'test';
              say $!blah;
          }
      }
  
      my $vwf = Vimwiki::File.new('t/test_file.md');
      say $vwf.^mro;
      say $vwf.s;
      say $vwf.blah;
  

  • the code outputs:

          hi
          test
          ((File) (Path) (Cool) (Any) (Mu))
          0
          (Any)
  

  • 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

• I wake up and check IRC
  • lizmat responded
    • yay!
    • suggested the IO::Path may not be subcasslifiable
      • suggested submitting report
      • issue submitted
        • Unable to subclass IO::Path · Issue #4750 · rakudo/rakudo: github.com
• I felt better and a lot less like a dummy

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

• lizmat has suggested a way for subclassing a core module
  • See Unable to subclass IO::Path · Issue #4750 · rakudo/rakudo: github.com
  • No delegation required
• End result that I'm going to build upon:

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

    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