Precious

Library to build value objects.

Why

• A value object is immutable
• A value object should have a whell known set of attributes
• A value object is equal to another value object if they are structurally equal aka if they have the same attributes with the same values

In PHP there are no primitives to obtain this, what you can do is to have objects with private properties, getters and a lot of boilerplate code.

Usage

<?php

use Precious\Precious;

final class Point extends Precious
{
    public static function from(int $x, int $y) : self
    {
        return new self(['x' => $x, 'y' => $y]);
    }

    protected function init() : array
    {
        return [
            self::required('x', self::integerType()),
            self::required('y', self::integerType()),
        ];
    }
}

$p1 = Point::from(1, 1);
$p2 = Point::from(1, 1);
$p3 = Point::from(2, 1);

assert($p1 == $p2);
assert($p1 != $p3);
assert($p1->x === $p2->x);
assert($p1->y === $p2->y);

$p4 = $p3->set('x', 1);
assert($p3 != $p4);
assert(spl_object_hash($p3) !== spl_object_hash($p4));
assert($p1 != $p3);
assert($p1 == $p4);

Installation

composer require gabrielelana/precious

PHPStan

Another problem of solutions where you generate properties based on some kind of definitions is that you will lose reference on the types of those properties (by defining accessor methods by hand you will not but you will have to write a lot of boilerplate code).

PHPStan support custom extensions that can be used to have the best of both solutions: avoid the boilerplate and keep the type information.

Install the suggested dependencies to use Precious at its full potential.

composer require --dev phpstan/phpstan
composer require --dev nikic/php-parser

If you also install phpstan/extension-installer with

composer require phpstan/extension-installer

then you're all set!

Otherwise follow the manual installation

If you don't want to use phpstan/extension-installer, add the custom rules in your project phpstan.neon file

includes:
  - %currentWorkingDirectory%/vendor/gabrielelana/precious/rules.neon

parameters:
  level: 7

then, this what you should expect

<?php

use Precious\Precious;

final class Point extends Precious
{
    public static function from(int $x, int $y) : self
    {
        return new self(['x' => $x, 'y' => $y]);
    }

    protected function init() : array
    {
        return [
            self::required('x', self::integerType()),
            self::required('y', self::integerType()),
        ];
    }
}

function doSomething() : void {
    $p = Point::from(1, 1);
    echo $p->x . PHP_EOL;
    echo $p->y . PHP_EOL;
    // Will raise: Access to an undefined property Point::$z
    echo $p->z . PHP_EOL;
    // Will raise: Property Point::$x is not writable
    $p->x = 2;
    // Will raise: Parameter #1 $s of function doSomethingWith expects string, int given
    doSomethingWith($p->x);
}

function doSomethingWith(string $s) : string {
    return $s;
}