The OptionsResolver Component

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The OptionsResolver Component

The OptionsResolver component helps you configure objects with option arrays. It supports default values, option constraints and lazy options.

Installation

You can install the component in 2 different ways:

Then, require the vendor/autoload.php file to enable the autoloading mechanism provided by Composer. Otherwise, your application won't be able to find the classes of this Symfony component.

Usage

Imagine you have a Mailer class which has 2 options: host and password. These options are going to be handled by the OptionsResolver Component.

First, create the Mailer class:

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class Mailer
{
    protected $options;

    public function __construct(array $options = array())
    {
    }
}

You could of course set the $options value directly on the property. Instead, use the OptionsResolver class and let it resolve the options by calling resolve(). The advantages of doing this will become more obvious as you continue:

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use Symfony\Component\OptionsResolver\OptionsResolver;

// ...
public function __construct(array $options = array())
{
    $resolver = new OptionsResolver();

    $this->options = $resolver->resolve($options);
}

The options property now is a well defined array with all resolved options readily available:

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// ...
public function sendMail($from, $to)
{
    $mail = ...;
    $mail->setHost($this->options['host']);
    $mail->setUsername($this->options['username']);
    $mail->setPassword($this->options['password']);
    // ...
}

Configuring the OptionsResolver

Now, try to actually use the class:

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$mailer = new Mailer(array(
    'host'     => 'smtp.example.org',
    'username' => 'user',
    'password' => 'pa$$word',
));

Right now, you'll receive a InvalidOptionsException, which tells you that the options host and password do not exist. This is because you need to configure the OptionsResolver first, so it knows which options should be resolved.

Tip

To check if an option exists, you can use the isKnown() function.

A best practice is to put the configuration in a method (e.g. configureOptions). You call this method in the constructor to configure the OptionsResolver class:

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use Symfony\Component\OptionsResolver\OptionsResolver;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

class Mailer
{
    protected $options;

    public function __construct(array $options = array())
    {
        $resolver = new OptionsResolver();
        $this->configureOptions($resolver);

        $this->options = $resolver->resolve($options);
    }

    protected function configureOptions(OptionsResolverInterface $resolver)
    {
        // ... configure the resolver, you will learn this
        // in the sections below
    }
}

Set default Values

Most of the options have a default value. You can configure these options by calling setDefaults():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setDefaults(array(
        'username' => 'root',
    ));
}

This would add an option - username - and give it a default value of root. If the user passes in a username option, that value will override this default. You don't need to configure username as an optional option.

Required Options

The host option is required: the class can't work without it. You can set the required options by calling setRequired():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    $resolver->setRequired(array('host'));
}

You are now able to use the class without errors:

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$mailer = new Mailer(array(
    'host' => 'smtp.example.org',
));

echo $mailer->getHost(); // 'smtp.example.org'

If you don't pass a required option, a MissingOptionsException will be thrown.

Tip

To determine if an option is required, you can use the isRequired() method.

Optional Options

Sometimes, an option can be optional (e.g. the password option in the Mailer class), but it doesn't have a default value. You can configure these options by calling setOptional():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setOptional(array('password'));
}

Options with defaults are already marked as optional.

Tip

When setting an option as optional, you can't be sure if it's in the array or not. You have to check if the option exists before using it.

To avoid checking if it exists everytime, you can also set a default of null to an option using the setDefaults() method (see Set Default Values), this means the element always exists in the array, but with a default of null.

Default Values that Depend on another Option

Suppose you add a port option to the Mailer class, whose default value you guess based on the encryption. You can do that easily by using a closure as the default value:

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use Symfony\Component\OptionsResolver\Options;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setDefaults(array(
        'encryption' => null,
        'port' => function (Options $options) {
            if ('ssl' === $options['encryption']) {
                return 465;
            }

            return 25;
        },
    ));
}

The Options class implements ArrayAccess, Iterator and Countable. That means you can handle it just like a normal array containing the options.

Caution

The first argument of the closure must be typehinted as Options, otherwise it is considered as the value.

Overwriting default Values

A previously set default value can be overwritten by invoking setDefaults() again. When using a closure as the new value it is passed 2 arguments:

  • $options: an Options instance with all the other default options
  • $previousValue: the previous set default value
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use Symfony\Component\OptionsResolver\Options;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...
    $resolver->setDefaults(array(
        'encryption' => 'ssl',
        'host' => 'localhost',
    ));

    // ...
    $resolver->setDefaults(array(
        'encryption' => 'tls', // simple overwrite
        'host' => function (Options $options, $previousValue) {
            return 'localhost' == $previousValue
                ? '127.0.0.1'
                : $previousValue;
        },
    ));
}

Tip

If the previous default value is calculated by an expensive closure and you don't need access to it, you can use the replaceDefaults() method instead. It acts like setDefaults but simply erases the previous value to improve performance. This means that the previous default value is not available when overwriting with another closure:

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use Symfony\Component\OptionsResolver\Options;
use Symfony\Component\OptionsResolver\OptionsResolverInterface;

// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...
    $resolver->setDefaults(array(
        'encryption' => 'ssl',
        'heavy' => function (Options $options) {
            // Some heavy calculations to create the $result

            return $result;
        },
    ));

    $resolver->replaceDefaults(array(
        'encryption' => 'tls', // simple overwrite
        'heavy' => function (Options $options) {
            // $previousValue not available
            // ...

            return $someOtherResult;
        },
    ));
}

Note

Existing option keys that you do not mention when overwriting are preserved.

Configure Allowed Values

Not all values are valid values for options. Suppose the Mailer class has a transport option, it can only be one of sendmail, mail or smtp. You can configure these allowed values by calling setAllowedValues():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setAllowedValues(array(
        'encryption' => array(null, 'ssl', 'tls'),
    ));
}

There is also an addAllowedValues() method, which you can use if you want to add an allowed value to the previously configured allowed values.

Configure Allowed Types

You can also specify allowed types. For instance, the port option can be anything, but it must be an integer. You can configure these types by calling setAllowedTypes():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setAllowedTypes(array(
        'port' => 'integer',
    ));
}

Possible types are the ones associated with the is_* PHP functions or a class name. You can also pass an array of types as the value. For instance, array('null', 'string') allows port to be null or a string.

There is also an addAllowedTypes() method, which you can use to add an allowed type to the previous allowed types.

Normalize the Options

Some values need to be normalized before you can use them. For instance, pretend that the host should always start with http://. To do that, you can write normalizers. These closures will be executed after all options are passed and should return the normalized value. You can configure these normalizers by calling setNormalizers():

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setNormalizers(array(
        'host' => function (Options $options, $value) {
            if ('http://' !== substr($value, 0, 7)) {
                $value = 'http://'.$value;
            }

            return $value;
        },
    ));
}

You see that the closure also gets an $options parameter. Sometimes, you need to use the other options for normalizing:

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// ...
protected function setDefaultOptions(OptionsResolverInterface $resolver)
{
    // ...

    $resolver->setNormalizers(array(
        'host' => function (Options $options, $value) {
            if (!in_array(substr($value, 0, 7), array('http://', 'https://'))) {
                if ($options['ssl']) {
                    $value = 'https://'.$value;
                } else {
                    $value = 'http://'.$value;
                }
            }

            return $value;
        },
    ));
}
This work, including the code samples, is licensed under a Creative Commons BY-SA 3.0 license.
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