icanboogie/accessor

Implements getters/setters, read-only/write-only properties, volatile defaults, type control…

v2.0.0 2018-11-25 16:30 UTC

README

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The icanboogie/accessor package allows classes to implement ICanBoogie's accessor design pattern. Using a combination of getters, setters, properties, and property visibilities, you can create read-only properties, write-only properties, virtual properties; and implement defaults, type control, guarding, and lazy loading.

Preamble

Because the package is a citizen of ICanBoogie's realm, which elected snake case a long time ago for its readability, the following examples use the same casing, but CamelCase is equally supported as we'll learn by the end of this document. Actually, because all getters and setters are formatted using the accessor_format trait method it is very easy to bind the formatting to one's requirements simply by overriding that method.

Getters and setters

A getter is a method that gets the value of a specific property. A setter is a method that sets the value of a specific property. You can define getters and setters on classes using the AccessorTrait trait, and optionally inform of its feature by implementing the HasAccessor interface.

Something to remember: Getters and setters are only invoked when their corresponding property is not accessible. This is most notably important to remember when using lazy loading, which creates the associated property when it is invoked.

Another thing to remember: You don't need to use getter/setter for everything and their cats, PHP is no Java, and it's okay to have public properties.

Read-only properties

Read-only properties are created by defining only a getter. A PropertyNotWritable exception is thrown in attempt to set a read-only property.

The following example demonstrates how a property read-only property can be implemented:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property-read mixed $property
 */
class ReadOnlyProperty
{
    use AccessorTrait;

    protected function get_property()
    {
        return 'value';
    }
}

$a = new ReadOnlyProperty;
echo $a->property;     // value
$a->property = null;   // throws ICanBoogie\PropertyNotWritable

An existing property can be made read-only by setting its visibility to protected or private:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property-read mixed $property
 */
class ReadOnlyProperty
{
    use AccessorTrait;

    private $property = "value";

    protected function get_property()
    {
        return $this->property;
    }
}

$a = new ReadOnlyProperty;
echo $a->property;     // value
$a->property = null;   // throws ICanBoogie\PropertyNotWritable

Protecting a construct property

Read-only properties are often used to provide read access to a property that was provided during construct, which should stay unchanged during the life time of an instance.

The following example demonstrates how a connection property passed during construct can only be read afterwards. The visibility of the property is set to private so that even an extending class cannot modify the property.

<?php

use ICanBoogie\Accessor\AccessorTrait;

class Connection
{
    //
}

/**
 * @property-read Connection $connection
 */
class Model
{
    use AccessorTrait;

    /**
     * @var Connection
     */
    private $connection;

    protected function get_connection()
    {
        return $this->connection;
    }

    protected $options;

    public function __construct(Connection $connection, array $options)
    {
        $this->connection = $connection;
        $this->options = $options;
    }
}

$connection = new Connection(…);
$model = new Model($connection, …);

$connection === $model->connection;   // true
$model->connection = null;            // throws ICanBoogie\PropertyNotWritable

Write-only properties

Write-only properties are created by defining only a setter. A PropertyNotReadable exception is thrown in attempt to get a write-only property.

The following example demonstrates how a property write-only property can be implemented:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property-write mixed $property
 */
class WriteOnlyProperty
{
    use AccessorTrait;

    protected function set_property($value)
    {
        //
    }
}

$a = new WriteOnlyProperty;
$a->property = 'value';
echo $a->property;   // throws ICanBoogie\PropertyNotReadable

An existing property can be made write-only by setting its visibility to protected or private:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property-write mixed $property
 */
class WriteOnlyProperty
{
    use AccessorTrait;
    
    private $property = 'value';

    protected function set_property($value)
    {
        $this->property = $value;
    }
}

$a = new WriteOnlyProperty;
$a->property = 'value';
echo $a->property;   // throws ICanBoogie\PropertyNotReadable

Virtual properties

A virtual property is created by defining a getter and a setter but no corresponding property. Virtual properties are usually providing an interface to another property or data structure.

The following example demonstrates how a minutes virtual property can be implemented as an interface to a seconds property.

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property int $minutes
 */
class Time
{
    use AccessorTrait;

    public $seconds;

    protected function set_minutes($minutes)
    {
        $this->seconds = $minutes * 60;
    }

    protected function get_minutes()
    {
        return $this->seconds / 60;
    }
}

$time = new Time;
$time->seconds = 120;
echo $time->minutes;   // 2

$time->minutes = 4;
echo $time->seconds;   // 240

Providing a default value until a property is set

Because getters are invoked when their corresponding property is inaccessible, and because an unset property is of course inaccessible, it is possible to define getters providing default values until a value is actually set.

The following example demonstrates how a default value can be provided while a property is inaccessible (unset an that case). During construct, if the slug property is empty it is unset, making it inaccessible. Thus, until the property is actually set, when the slug property is read its getter is invoked and returns a default value created from the title property.

<?php

use ICanBoogie\Accessor\AccessorTrait;

class Article
{
    use AccessorTrait;

    public $title;
    public $slug;

    public function __construct($title, $slug = null)
    {
        $this->title = $title;

        if ($slug)
        {
            $this->slug = $slug;
        }
        else
        {
            unset($this->slug);
        }
    }

    protected function get_slug()
    {
        return \ICanBoogie\normalize($this->slug);
    }
}

$article = new Article("This is my article");
echo $article->slug;   // this-is-my-article
$article->slug = "my-article";
echo $article->slug;   // my-article
unset($article->slug);
echo $article->slug;   // this-is-my-article

Façade properties (and type control)

Sometimes you want to be able to manage the type of a property, what can be stored, what can be retrieved, the most transparently possible. This can be achieved with façade properties.

Façade properties are implemented by defining a private property along with its getter and setter.

The following example demonstrates how a created_at property is implemented. It can be set to a mixed value, but is always read as a DateTime instance.

<?php

use ICanBoogie\Accessor\AccessorTrait;
use ICanBoogie\DateTime;

/**
 * @property DateTime $created_at
 */
class Article
{
    use AccessorTrait;

    private $created_at;

    protected function set_created_at($datetime)
    {
        $this->created_at = $datetime;
    }

    protected function get_created_at()
    {
        $datetime = $this->created_at;

        if ($datetime instanceof DateTime)
        {
            return $datetime;
        }

        return $this->created_at = ($datetime === null) ? DateTime::none() : new DateTime($datetime, 'utc');
    }
}

Façade properties are exported on serialization

Although façade properties are defined using private properties, they are exported when the instance is serialized, just like they would if they were public or protected.

<?php

$article = new Article;
$article->created_at = 'now';

$test = unserialize(serialize($article));
echo get_class($test->created_at);           // ICanBoogie/DateTime
$article->created_at == $test->created_at;   // true

Lazy loading

Lazy loading creates the associated property when it is invoked, making subsequent accesses using the property rather than the getter.

In the following example, the lazy_get_pseudo_uniqid() getter returns a unique value, but because the pseudo_uniqid property is created with the public visibility after the getter was called, any subsequent access to the property returns the same value:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property string $pseudo_uniqid
 */
class PseudoUniqID
{
    use AccessorTrait;

    protected function lazy_get_pseudo_uniqid()
    {
        return uniqid();
    }
}

$a = new PseudoUniqID;

echo $a->pseudo_uniqid; // 5089497a540f8
echo $a->pseudo_uniqid; // 5089497a540f8

Of course, unsetting the created property resets the process.

<?php

unset($a->pseudo_uniqid);

echo $a->pseudo_uniqid; // 508949b5aaa00
echo $a->pseudo_uniqid; // 508949b5aaa00

Setting a lazy property

Lazy properties are implemented similarly to read-only properties, by defining a method to get a value, but unlike read-only properties lazy properties can be written too:

<?php

$a = new PseudoUniqID;

echo $a->pseudo_uniqid;   // a009b3a984a50
$a->pseudo_uniqid = 123456;
echo $a->pseudo_uniqid;   // 123456

unset($a->pseudo_uniqid);
echo $a->pseudo_uniqid;   // 57e5ada092180

You need to remember that lazy properties actually create a property, thus the getter won't be invoked if the property is already accessible.

Overloading getters and setters

Because getters and setters are classic methods, they can be overloaded. That is, the setter or getter of a parent class can be overloaded by an extending class.

The following example demonstrates how an Awesome class extending an Plain class can turn a plain getter into an awesome getter:

<?php

use ICanBoogie\Accessor\AccessorTrait;

/**
 * @property-read string $property
 */
class Plain
{
    use AccessorTrait;
    
    protected function get_property()
    {
        return "value";
    }
}

class Awesome extends Plain
{
    protected function get_property()
    {
        return "awesome " . parent::get_property();
    }
}

$plain = new Plain;
echo $plain->property;     // value

$awesome = new Awesome;
echo $awesome->property;   // awesome value

CamelCase support

CamelCase getters and setters are equally supported. Instead of using the AccessorTrait, use the AccessorCamelTrait:

<?php

use ICanBoogie\Accessor\AccessorCamelTrait;

/**
 * @property-read $camelProperty
 */
class CamelExample
{
    use AccessorCamelTrait;
    
    private $camelProperty;
    
    protected function getCamelProperty()
    {
        return $this->camelProperty;
    }
    
    public function __construct($value)
    {
        $this->camelProperty = $value;
    }
}

$a = new CamelExample("value");
echo $a->camelProperty;   // value

Requirements

The package requires PHP 5.6 or later.

Installation

The recommended way to install this package is through Composer:

$ composer require icanboogie/accessor

Documentation

The package is documented as part of the ICanBoogie framework documentation. You can generate the documentation for the package and its dependencies with the make doc command. The documentation is generated in the build/docs directory. ApiGen is required. The directory can later be cleaned with the make clean command.

Testing

The test suite is ran with the make test command. PHPUnit and Composer need to be globally available to run the suite. The command installs dependencies as required. The make test-coverage command runs test suite and also creates an HTML coverage report in "build/coverage". The directory can later be cleaned with the make clean command.

To ensure tests are running with the minimum requirements, it is advised to run them inside the provided container. The container is started with the make test-container command. Once inside the container, make test and make test-coverage can be used. Xdebug is available in the container and ready for debugging, it uses the servername accessor-tests and the absolute path /app.

The package is continuously tested by Travis CI.

Build Status Code Coverage

License

icanboogie/accessor is licensed under the New BSD License. See the LICENSE file for details.