Ron Buckton rbuckton

Pattern Matching Exploration

The following sections explore various ways we could consider introducing pattern matching to ECMAScript, and can be used to inform a discussion on how best to layer the proposal. The various explorations in this document are not intended to be taken as a whole, as some sections directly conflict with others. Any exploration will specifically call out other explorations that are related.

This list is by no means complete. Suggestions for additions or changes are welcome.

Extending Existing Syntax

Pattern Matching Tenets

Patterns should be [concise][]
Patterns should be [expressive][]
Patterns should be [explicit][]
Patterns should be [extensible][]
Pattern matching should be [exhaustive][]

Tenet 1 — Patterns should be concise

Notational Conventions

Examples in this document may use ECMAScript internal-values as specified in https://tc39.es/ecma262/#sec-value-notation. Such values will appear in ECMAScript examples as ~value-name~ and are not intended to denote new synatx.

This document uses abstract operations defined either in https://github.com/tc39/proposal-pattern-matching or in this document. Such abstract operations will be differentiated from normal ECMAScript functions by names like %OperationName% and are not intended to denote new syntax.

Portions of this document are enclosed in block-quotes. These sections reference portions of https://github.com/codehag/pattern-matching-epic.

If I were to change the definition of @@toEnum slightly, we could build ADT-style enums into https://github.com/rbuckton/proposal-struct.

Currently, @@toEnum takes three arguments: key, value and autoValue. If we change this to take a more complex context argument, we have more flexibility:

interface ValueEnumFactoryContext {
    base: typeof Enum;
    name: string | symbol;
    kind: "value";

`__classPrivateFieldSet`

var __classPrivateFieldSet = (this && this.__classPrivateFieldSet) || function (receiver, state, value, kind, f) {
    if (kind === "method") throw new TypeError("Private method is not writable");
    if (kind === "accessor" && !f) throw new TypeError("Private accessor was defined without a setter");
    if (typeof state === "function" ? receiver !== state || !f : !state.has(receiver)) throw new TypeError("Cannot write private member to an object whose class did not declare it");
    return (kind === "accessor" ? f.call(receiver, value) : f ? f.value = value : state.set(receiver, value)), value;
};

Based on list of Regular Expression Engines from https://en.wikipedia.org/wiki/Comparison_of_regular-expression_engines

Engine	Language	Flags	Note
[Boost.Regex][]	C++	[`imsx`][Boost.Regex(flags)]
[DEELX][]	C++	[`imsg`][DEELX(flags)]
[Glib/GRegex][]	C++	[`imsx`][Glib/GRegex(flags)]
[GRETA][]	C++		Could not find documentation.
[Gregex][]	RTL, HLS		Could not find documentation.
[RXP][]	RTL		Could not find documentation.

Grouped Accessors and Auto-Accessors for ECMAScript classes and Object Literals

This introduces new syntax for grouped accessors and auto-accessors to classes and object literals. A grouped accessor is a single declaration that contains either or both both of the get and set methods for an accessor. An auto-accessor is a simplified variant of a grouped accessor that elides the bodies of the get and set methods and introduces a private backing field used by both the getter and setter.

	const fs = require("fs");
	const path = require("path");
	const delay = (ms) => new Promise(resolve => setTimeout(resolve, ms));
	async function main() {
	console.log("Setting up real/link folders...");
	try { fs.mkdirSync(path.join(__dirname, "real/sub/folder"), { recursive: true }); } catch { }
	try { fs.unlinkSync(path.join(__dirname, "real/sub/folder/test.txt")); } catch { }
	try { fs.symlinkSync(path.join(__dirname, "real"), path.join(__dirname, "link"), "junction"); } catch { }

	await delay(1_000);

	;FLAVOR:Marlin
	;Printer: Ender 3 Pro

	;; Copyright 2023 Ron Buckton
	;; Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated
	;; documentation files (the “Software”), to deal in the Software without restriction, including without limitation the
	;; rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to
	;; permit persons to whom the Software is furnished to do so, subject to the following conditions:
	;;
	;; The above copyright notice and this permission notice shall be included in all copies or substantial portions of the

	// a simple SafeHandle with a public `dangerousGetHandle` method.
	class SafeHandle {
	static #finalizer = new FinalizationRegistry(({ handle, releaseHandle }) => {
	releaseHandle(handle);
	});

	#data = null;

	constructor(handle, releaseHandle) {
	this.#data = { handle, releaseHandle };