ADT (Algebraic Data Types)

Poor man's implementation of Algebraic Data Types in PHP.

Also known as an enum with an associated value in other languages like Swift or Rust.

Installation

Install with composer at krak/adt

Usage

<?php

use Krak\ADT\ADT;

/**
 * @method static Upc upc(int $numberSystem, int $manufacturer, int $product, int $check)
 * @method static QrCode qrCode(string $productCode)
 */
abstract class Barcode extends ADT {
    public static function types(): array {
        return [Upc::class, QrCode::class];
    }
}

final class Upc extends Barcode {
    public $numberSystem;
    public $manufacturer;
    public $product;
    public $check;

    public function __construct(int $numberSystem, int $manufacturer, int $product, int $check) {
        $this->numberSystem = $numberSystem;
        $this->manufacturer = $manufacturer;
        $this->product = $product;
        $this->check = $check;
    }
}

final class QrCode extends Barcode {
    public $productCode;

    public function __construct(string $productCode) {
        $this->productCode = $productCode;
    }
}

$barcode = new QrCode('abc123');

// requires that all cases are set or exception is thrown
$oneOrTwo = $barcode->match([
    Upc::class => function(Upc $upc) { return 1;},
    QrCode::class => function(QrCode $qrCode) { return 2; },
]);

// allow a default value
$oneOrNull = $barcode->matchWithDefault([
    Upc::class => function(Upc $upc) { return 1; }
]);

// return static values
$threeOrFour = $barcode->match([
    Upc::class => 3,
    QrCode::class => 4,
]);

// static constructors
$qrCode = Barcode::qrCode('abc123');

Autoloading Concerns

With the example above, if you try to create a QrCode or Upc before ever referencing the Barcode class, you'll likely get a file not found when using composer's psr-4 autoloader.

You can get around this a few ways:

1. Utilize class mapping

2. Include the enum class file in the composer autoload.files section (something like php-inc could make that easier)

3. Utilize static constructors provided by the base ADT class:

   <?php
   
   $upc = Barcode::upc(1, 2, 3, 4);
   $qrCode = Barcode::qrCode('abc123');

Tests

Tests are run via make test and are stored in the test directory. We use peridot for testing.