jakewhiteley/hodl

A lightweight dependency injection cointainer for PHP, which sites inbetween Pimple and the Laravel Container

Hodl DI

, _(*1)

Hodl provides full autowiring capabilities for Inversion of Control, but is simple enough to use as a standalone service container without any faff., _(*2)

It's a simple ArrayAccess Service container which takes inspiration from both Laravel and Pimple (Symfony), but sits comfortably in the middle., _(*3)

Basic Usage

A service can be added to the container by providing the class name, and a definition for the service., _(*4)

```` php $hodl->add('Some\Namespace\Foo', function() { return new Foo(); });, <sub>(*5)</sub>

You should always register a service using it's full class name. This is so that the autowiring can work and classes can have their dependencies injected with no fuss.

### Retrieving a service

As simple as it gets:

```` php
$foo = $hodl->get('Some\Namespace\Foo');

Checking if a service exists

As all services are referenced by the key you defined it with, you can use has() to check if that key has been defined previously:, <sub>(*6)</sub>

```` php use Namespace\Foo;, <sub>(*7)</sub>

// using the ::class shorthand $hodl->add(Foo::class, function() { return new Foo(); });, <sub>(*8)</sub>

$hodl->has(Foo::class); // true $hodl->has('some\other\class'); // false, <sub>(*9)</sub>

### Removing services

As the Container implements ArrayAccess you can use `unset()` or the `remove()` method to remove a class:

```` php
$hodl['foo'] = function(){
    return new Foo();
};

$hodl->has('foo'); // true

$hodl->remove('foo');

$hodl->has('foo'); // false

Removing a service will also remove any aliases or bound interfaces as well (more on that below)., <sub>(*10)</sub>

ArrayAccess style

As Hodl implements ArrayAccess, you can achieve the above like this instead:, <sub>(*11)</sub>

// add
$hodl['Some\Namespace\Foo'] = function(){
    return new Foo();
};

// get
$foo = $hodl['Some\Namespace\Foo'];

// check
if (isset($hodl['Some\Namespace\Foo')) // ...

// remove
unset($hodl['Some\Namespace\Foo']);

Service definitions

When adding a new service definition, the callable which returns the class is passed an instance of Hodl, which can be used for passing arguments derived from services already within the container. Note You should not pass services directly into the constructor of your service. For that we have the magic of autowiring., <sub>(*12)</sub>

```` php $hodl->get('Baz', function($hodl) { return new Baz($hodl->get('Some\Namespace\Foo')->someProp); });, <sub>(*13)</sub>

## Singletons

The above examplse will return a new instance of the service no matter when it is fetched.
You can also specify that the same instance should be returned each time by using the `addFactory()` method:

```` php
$hodl->addSingleton(Bar::class, function() {
    return new Bar();
});

Instances

You can also add a specific instance as a service. As this is already booted, Hodl can derrive the class name pretty easily so there is no need to supply that., <sub>(*14)</sub>

$instance = new Foo\Bar();
$instance->prop = 'foobar';

$hodl->addInstance($instance);

// ...

$hodl->get('Foo\Bar')->prop // equals 'foobar'

Aliases

Sometimes it is tiresome typing in fully qualified class names to get access to a service. Luckily you can also define an alias to a service for quick retrieval:, <sub>(*15)</sub>

```` php // using the ::class shorthand $hodl->add(Foo::class, function() { return new Foo(); });, <sub>(*16)</sub>

// Adda alias. $hodl->alias(Foo:class, 'myAlias');, <sub>(*17)</sub>

$hodl->has(Foo::class); // true $hodl->has('myAlias'); // true, <sub>(*18)</sub>

#### Removing aliases
If at somepoint you need to remove an alias, or binding (see below) then you can use the `removeAlias($alias)` method.

## Autowiring (resolving dependencies)

Aside as using it as a container for passing objects around, it can also be used to auotmatically resolve objects using the Reflection API and achieve Inversion of Control.

Consider the following object:

```` php
namespace Foo;

class Foo
{
    function __construct( Bar $bar )
    {
        $this->bar = $bar;
    }
}

When this object is created, it needs to be passed an instance of Foo\Bar as the first argument., <sub>(*19)</sub>

Using the resolve() method this is super easy:, <sub>(*20)</sub>

```` php $foo = $hodl->resolve('Foo\Foo');, <sub>(*21)</sub>

The object will be created an an instance of `Foo\Bar` will be initialized and passed through automatically. 

This works recursively so any dependencies of `Foo\Bar` will be magically resolved as well.

### Passing arguments

The resolve method also accepts a second argument, which is an array of extra parameters you want to pass to the object constructors.

The keys of this array must be the variable name of the parameter.

```` php
// using the Foo class in the previous example, but with a following constructor:
// function __construct( Bar $bar, int $someInt, string $someString = 'string' ) { ...

// by not passing someString as a key, the default of 'string' will be used
$foo = $hodl->resolve('Foo\Foo', [
    'someInt' => 42
]);

Resolving using services

The above examples have an empty container, so all services are injected as new generic instances of that class. But if a service exists within the container, that service will be used instead - allowing your specific instance or a persistent object to be passed to any object which needs it., <sub>(*22)</sub>

class Foo
{
    public $var = 'foo';
}

class Bar
{
    public $foo;

    public function __construct(Foo $foo)
    {
        $this->foo = $foo;
    }
}

// Add Foo as a singleton
$hodl->addSingleton('Foo', function() {
    return new Foo();
});

$hodl['Foo']->var = 'changed!';


$var = $hodl->resolve('Bar')->foo->var; // equals 'changed!'

Don't be afraid to use resolve() when adding a service definition to the container either!, <sub>(*23)</sub>

```` php $hodl->add('Bar', function($hodl) { return $hodl->resolve('Bar'); // All of Bar's dependencies will be injected as soon as it is fetched });, <sub>(*24)</sub>

### Binding implementations to interfaces

A really useful feature when using the autowiring functionality is to be able to specify in a constructor an interface, and have Hodl deal with passing the correct implementation to the resolved class.

Consider the following:

```` php
// Basic interface
interface HelloWorld
{
    public function output();
}

// Service
class NeedsResolving
{
    public function __construct(HelloWorld $writer)
    {
        $this->writer = $writer;
    }

    public function output()
    {
        $this->writer->output();
    }
}

We know the NeedsResolving class needs some kind of HelloWorld implementation to actually work. We can let Hodl know which one using the bind() method:, <sub>(*25)</sub>

```` php class MyPrinter implements HelloWorld { public function output() { echo 'Hello world!'; } }, <sub>(*26)</sub>

$hodl->bind(MyPrinter::class, HellowWorld::class);, <sub>(*27)</sub>

// Correctly gets an instance of MyPrinter $foo = $hodl->resolve(NeedsResolving::class);, <sub>(*28)</sub>

$foo->output(); // Outputs 'Hello world!', <sub>(*29)</sub>

#### Removing bindings
As under the hood `bind()` as an alias for `alias()`, the `removeAlias($interface)` method will remove a binding. Useful if for whatever reason you had to hot-swap an implementation out for another.

## Resolving methods
The `resolveMethod($class, $methodName, $args)` method allows autowiring of class members the same way that `resolve()` works on classes.

````php
$hodl->resolveMethod(Foo::class, 'someMethod');

resolveMethod will call the supplied method, recursively inject dependencies and allow you to pass extra non-object parameters as per the resolve examples above. This works on static methods as well as public ones., <sub>(*30)</sub>

Resolving instance methods

The example above shows someMethod being execcuted and returned on a new instance of Foo, but you can also pass a specific instance instead of the class name:, <sub>(*31)</sub>

$foo = new Foo();
$return = $hodl->resolveMethod($foo, 'someMethod', ['amount_of_awesome' => 100]);

Both resolve and resolveMethod could therefore be used together to create a new fully resolved object and execute a method., <sub>(*32)</sub>

class Bar
{
    public $foo;

    public function __construct(Foo $foo)
    {
        $this->foo = $foo;
    }

    public function methodName(Foo\Baz $baz)
    {
        return $this->foo->var * $baz->var;
    }
}

// Fully resolves methodName and returns an instance of Foo\Baz
$resolvedBaz = $hodl->resolveMethod(
    $hodl->resolve('Bar'),
    'methodName'
);

Conclusion

By adding services to Hodl, your code can achieve complete inversion of control and manage classes application-wide with no need for a single new keyword or singleton in sight., <sub>(*33)</sub>

Contributing

If you have any improvements, bugs, or feature requests; feel free to open up an issue or PR., <sub>(*34)</sub>