Dynamically instantiating a class based on string in PHP

Question

Im currently getting my hands dirty with some subclassing object oriented php. I would like to use an array to create some form fields, and these fields are separated into classes based on their type. This means that I have a main class called "form_field", and then have a bunch of subclasses called "form_field_type" (ex. "form_field_select"). The idea is that each subclass "knows" how to best generate their HTML in a display method.

So lets say that i write an array like this:

$fields = array(
    array(
        'name' => 'field1',
        'type' => 'text',
        'label' => 'label1',
        'description' => 'desc1',
        'required' => true,
    ),
    array(
        'name' => 'field2',
        'type' => 'select',
        'label' => 'label1',
        'description' => 'desc1',
        'options' => array(
                'option1' => 'Cat',
                'option2' => 'Dog',
            ),
        'ui' => 'select2',
        'allow_null' => false,
    )
);

I would then like to create a loop that instantiates the correct class based on the type:

foreach ($fields as $field) {
    $type = $field['type'];

    $new_field = // instantiate the correct field class here based on type

    $new_field->display();
}

What would be the best approach here? I would like to avoid doing something like:

if ($type == 'text') {
    $new_field = new form_field_text();
} else if ($type == 'select') {
    $new_field = new form_field_select();
} // etc...

This just feels inefficient, and i feel like there must be a better way? Is there a good pattern that is generally used in this situation, or am I going about solving this the wrong way?

I think you should take a look on the factory design pattern. — Sascha
– Sascha, Commented Sep 21, 2014 at 14:38

algorhythm · Accepted Answer · 2014-09-21 14:39:22Z

1

Try something like this...

foreach ($fields as $field) {
    $type = $field['type'];

    // instantiate the correct field class here based on type
    $classname = 'form_field_' .$type;
    if (!class_exists($classname)) { //continue or throw new Exception }

    // functional
    $new_field = new $classname();

    // object oriented
    $class = new ReflectionClass($classname);
    $new_field = $class->newInstance();

    $new_field->display();
}

edited Sep 21, 2014 at 14:39

answered Sep 21, 2014 at 14:33

algorhythm

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