Typed Doctrine Collections

Type hinting is evolving but PHP 7 still does not currently provide a way to define the type of the elements of an array (a.k.a. Generics.)

This library is built on top of Doctrine/Collections to enforce type checking on elements added to a collection. We could also call them strongly typed arrays.

The aim is to leverage type hinting to help prevent bugs, or, at the very least, detect them earlier in the development cycle.

For the purpose of this library, the term type is used loosely to refer to built-in PHP types, classes, and even application-domain types.

Installation

composer require jausions/php-typed-doctrine-collections

In the examples below, the require 'vendor/autoload.php'; is implied.

Type Defined by Initial Value

The first element passed to the constructor determines the criteria for the elements that come after it.

<?php
use Abacus11\Doctrine\Collections\CollectionOf;

$int_array = new CollectionOf([1, 2]);      // Okay
$int_array = new CollectionOf([1, '2']);    // Not okay - throws \TypeError
$int_array = new CollectionOf([null, 1]);   // Not okay - throws \InvalidArgumentException

Type Defined by a Sample Value

The element validation is done against the type of a sample value.

<?php
use Abacus11\Doctrine\Collections\CollectionOf;

$sample = 1;
$int_array = (new CollectionOf())->setElementTypeLike($sample);

$int_array[] = 2;              // Okay
$int_array[] = true;           // Not okay - throws \TypeError exception

class SomeClass {}

$sample = new SomeClass();
$some = (new CollectionOf())->setElementTypeLike($sample);

$some[] = new SomeClass();     // Okay
$some[] = new stdClass();      // Not okay - throws \TypeError exception

Type Defined by a Closure

The elements added to the collection can be checked with a closure:

<?php
use Abacus11\Doctrine\Collections\CollectionOf;

// Use the setElementType() method

$positive_int = (new CollectionOf())->setElementType(function ($value) {
    if (!is_integer($value)) {
        return false;
    }
    return ($value >= 0);
});

$positive_int['apples'] = 0;      // Okay
$positive_int['oranges'] = 10;    // Okay
$positive_int['bananas'] = -5;    // Not okay - throws \TypeError exception

// Or directly in the constructor

$negative_int = new CollectionOf(
    function ($value) {
        if (!is_integer($value)) {
            return false;
        }
        return ($value <= 0);
    }
);

$negative_int[] = -50;            // Okay
$negative_int[] = 5;              // Not okay - throws \TypeError exception

Type Defined by a Class Name

Objects added to the collection can be checked against a class name:

<?php

use Abacus11\Doctrine\Collections\CollectionOf;

class A {}

class B {}

class AA extends A {}

// Use the setElementType() method

$some_a = (new CollectionOf())->setElementType(A::class);

$some_a[] = new A();    // Okay
$some_a[] = new AA();   // Okay
$some_a[] = new B();    // Not okay - throws \TypeError exception

// Or directly in the constructor

$some_b = new CollectionOf(B::class);

$some_b[] = new B();    // Okay
$some_b[] = new A();    // Not okay - throws \TypeError exception

Built-In Library Types

Apart from a closure or a class name, the setElementType() method also accepts the following values:

• array
• boolean
• callable
• double
• integer
• number
• json
• object
• resource
• string

<?php
use Abacus11\Doctrine\Collections\CollectionOf;

// Use the setElementType() method

$int_array = (new CollectionOf())->setElementType('integer');

$int_array[] = 1;      // Okay
$int_array[] = '1';    // Not okay - throws \TypeError exception

// Or directly in the constructor

$int_array = new CollectionOf('integer');

$int_array[] = 20;     // Okay
$int_array[] = true;   // Not okay - throws \TypeError exception

Built-In Collections

Several typed collections are predefined:

• \Abacus11\Doctrine\Collections\Arrays
• \Abacus11\Doctrine\Collections\Booleans
• \Abacus11\Doctrine\Collections\Callables
• \Abacus11\Doctrine\Collections\Doubles
• \Abacus11\Doctrine\Collections\Integers
• \Abacus11\Doctrine\Collections\Numbers
• \Abacus11\Doctrine\Collections\JSONs
• \Abacus11\Doctrine\Collections\Objects
• \Abacus11\Doctrine\Collections\Resources
• \Abacus11\Doctrine\Collections\Strings

<?php
$integers = new \Abacus11\Doctrine\Collections\Integers([1, 2, 3, 0, -1]);

Custom Type Collections

You can easily create collections by extending the base class or by including the trait into your own implementation of the ArrayAccess interface.

<?php
use Abacus11\Doctrine\Collections\CollectionOf;

class Vehicle
{
}

class Car extends Vehicle
{
    public $make;
    public $model;
    public $color;
    public $license_plate_number;
}

class Submarine extends Vehicle
{
    public $name;
}

class Cars extends CollectionOf
{
    /**
     * @param Car[] $cars
     */
    public function __construct(array $cars = []) {
        parent::__construct(Car::class, $cars);
        // - or -
        //$this->setElementType(Car::class);
        //parent::__construct($cars);
    }
}

class Parking
{
    /**
     * @var Cars
     */
    protected $lot;

    public function __construct()
    {
        $this->lot = new Cars([]);
    }

    public function enter(Vehicle $car)
    {
        $this->lot[] = $car;
    }

    /**
     * @return Car[] The collection of cars
     */
    public function getCars(): Cars
    {
        return $this->lot;
    }

    //...
}

$my_car = new Car();
$my_car->model = 'T';
$my_car->make = 'Ford';
$my_car->color = 'Black';
$my_car->license_plate_number = 'MI-01234';

$my_sub = new Submarine();
$my_sub->name = 'Nautilus';

$parking = new Parking();
$parking->enter($my_car);   // Okay
$parking->enter($my_sub);   // Not okay - throws \TypeError exception

Remarks:

1. We could have type hinted the enter() method with the Car class instead of the Vehicle class. This would also have thrown a \TypeError exception.
2. I am aware that I mixed the types in the docBlock and the signature of the getCars() method. It is somewhat more legible and may help your IDE. However, the benefit may vary depending on your editor / IDE, and it may lead to confusion if trying to use some array function that expect a native array type.