https://www.reddit.com/r/PHPhelp/comments/62oown/is_there_anything_bad_about_1_function_per_file/

extendedStaticMethods.php

<?php

/**
 * Class Base
 */
Class Base {
    /**
     * @param $name
     * @return string
     */
    public static function hello($name) {
        return sprintf('Hello, %s!', $name);
    }
}

/**
 * Class Extended
 */
Class Extended extends Base {

    /**
     * @param $name string
     * @return string
     */
    public static function hello($name = null) {
        if (null === $name) {
            $name = 'World';
        }
        return parent::hello($name);
    }
}

/**
 * Class ExtendedLegacy
 */
Class ExtendedLegacy extends Base {

    /**
     * @param $name string
     * @return string
     */
    public static function hello($name = null) {
        if (null === $name) {
            $name = 'Universe';
        }
        return sprintf('Hello, %s!', ucwords($name));
    }
}

$emptyName = null;
$name = 'bob';

echo '=== Base ===' . PHP_EOL;
echo Base::hello($emptyName) . PHP_EOL;
echo Base::hello($name) . PHP_EOL;

echo '=== Extended ===' . PHP_EOL;
echo Extended::hello($emptyName) . PHP_EOL;
echo Extended::hello($name) . PHP_EOL;

echo '=== ExtendedLegacy ===' . PHP_EOL;
echo ExtendedLegacy::hello($emptyName) . PHP_EOL;
echo ExtendedLegacy::hello($name) . PHP_EOL;

The following example outputs:

=== Base ===
Hello, !
Hello, bob!
=== Extended ===
Hello, World!
Hello, bob!
=== ExtendedLegacy ===
Hello, Universe!
Hello, Bob!