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shrikeh/collections
===================

Traits for re-use in immutable collections

v1.0.4(9y ago)11.5kMITPHP

Since Oct 13Pushed 9y ago2 watchersCompare

[ Source](https://github.com/shrikeh/php-immutable-collections)[ Packagist](https://packagist.org/packages/shrikeh/collections)[ RSS](/packages/shrikeh-collections/feed)WikiDiscussions master Synced 2mo ago

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php-immutable-collections
=========================

[](#php-immutable-collections)

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Trait-based helper library to take care of the heavy lifting of immutable collections in PHP.

Overview
--------

[](#overview)

This low-level library is just time-saving [traits](http://php.net/manual/en/language.oop5.traits.php "Link to traits overview in PHP 5.4") for creating immutable collections. As PHP 7 can use [return type hinting](http://php.net/manual/en/functions.returning-values.php "PHP 7 Returning Values"), I decided I would always return a Collection if there was a possibility of returning *0-n* objects from a method, and could then type hint the return value as a Collection, whether empty or not. PHP does not natively support immutable iterators, so I find that whenever I use [Domain-Driven Design](https://en.wikipedia.org/wiki/Domain-driven_design "Domain driven design definition"), and need an iterable list of [Value Objects](https://en.wikipedia.org/wiki/Value_object "Value Objects definition"), I have to do the same boilerplate re-work.

This pattern has been successful for me, as I can also strongly type the Collections themselves, so they can only contain objects of a given type. I also generally make them immutable, so they throw a descendent of [`DomainException`](http://php.net/manual/en/class.domainexception.php "PHP Domain Exception documentation") if you try to set or unset a value.

So as I use these more often, I split them up into Traits for re-use across my code. Feel free to use for yourself, they're tiny and just take care of boilerplate stuff for me.

Installation
------------

[](#installation)

Recommended installation is via the ubiquitous and seminal [`composer`](https://getcomposer.org/ "Link to composer website"):

```
composer require --prefer-dist shrikeh/collections
```

Usage
-----

[](#usage)

The library consists of about a dozen traits that aid in matching core PHP and SPL interfaces such as [`ArrayAccess`](http://php.net/manual/en/class.arrayaccess.php "The ArrayAccess interface") and [`OuterIterator`](http://php.net/manual/en/class.outeriterator.php "The OuterIterator interface"). Generally I have an inner "storage", and ensure that access to this directly is removed, including mutable methods such as `offSetSet()` or `offsetUnset()`. This ensures that only the values added to the constructor can be iterated over.

As an example, to create a Collection that can only contain `SomeObject` objects:

```