StringList for PHP

StringList.php

<?php

class StringList extends \ArrayObject
{
    protected $data = [];

    public function __construct($data, $delimiter = " ")
    {
        self::checkNonScalarValues($data);

        if (self::isIterable($data)) {
            $this->data = $data;
        } else {
            $this->data = explode($delimiter, $data);
        }

        $this->delimiter = $delimiter;
        parent::__construct($this->data);
    }

    protected static function checkNonScalarValues($data)
    {
        if (self::isIterable($data) == true) {
            foreach ($data as $value) {
                self::checkNonScalarValues($value);
            }
        } elseif (is_scalar($data) == false) {
            throw new \InvalidArgumentException("Cannot convert first parameter to string");
        }
    }

    protected static function isIterable($data)
    {
        return is_array($data) || ($data instanceof \Traversable);
    }

    public function __toString()
    {
        return implode($this->delimiter, $this->data);
    }
}

For type-hinting parameters that can either be string or array.

Instead of checking the parameter if iterable..

function setTags($tags)
{
    if (is_array($tags) == false) {
        $tags = explode(',', $tags);
    }

    foreach ($tags as $tag) {
        // do stuff here
    }
}

setTags("foo,bar,baz");
// or
setTags(["foo","bar","baz"]);

You can just type-hint the parameter with StringList

function setTags(StringList $tags)
{
    foreach ($tags as $tag) {
        // do stuff here
    }
}

$tags = new StringList("foo,bar,baz", ",");
// or
$tags = new StringList(["foo","bar","baz"], ",");

setTags($tags);

You can also create a StringList inside the method

function setTags($tags)
{
    $tags = new StringList($tags, ",");

    foreach ($tags as $tag) {
        // do stuff here
    }
}

setTags("foo,bar,baz");
// or
setTags(["foo","bar","baz"]);

The advantage of this is you can type-hint StringList on your methods.
Making sure of what parameter is passed instead of validating it manually.