Custom dropdown field that pretends to submit an array (but only allows selection of one item)

SingleSelectListBoxDropdownField.php

<?php

namespace App\Forms;

use SilverStripe\Forms\DropdownField;

class SingleSelectListBoxDropdownField extends DropdownField
{
    /**
     * Force this field to appear as if it saves an array
     * 
     * @return array
     */
    public function getAttributes()
    {
        return array_merge(
            parent::getAttributes(),
            array(
                'size' => 1,
                'name' => $this->getName() . '[]'
            )
        );
    }

    /**
     * Validate this field
     *
     * @param Validator $validator
     * @return bool
     */
    public function validate($validator)
    {
        // Check if valid value is given
        $selected = $this->Value()[0];
        if (strlen($selected)) {
            // Use selection rules to check which are valid
            foreach ($this->getValidValues() as $formValue) {
                if ($this->isSelectedValue($formValue, $selected)) {
                    return true;
                }
            }
        } else {
            if ($this->getHasEmptyDefault()) {
                // Check empty value
                return true;
            }
            $selected = '(none)';
        }

        // Fail
        $validator->validationError(
            $this->name,
            _t(
                'SilverStripe\\Forms\\DropdownField.SOURCE_VALIDATION',
                "Please select a value within the list provided. {value} is not a valid option",
                array('value' => $selected)
            ),
            "validation"
        );
        return false;
    }
}