README

A PSR-11 compliant Dependency Inversion Container

Why another container implementation?

The primary motivation for creating this was to have a container implementation that's optimized for containerized deployment in a long-running process (like ReactPHP and PHP-PM).

The usage and API is is highly inspired by PHP-DI, but adds functionality to support factories at definition-time (rather than exclusively at access-time with make). This is intended to reduce unpredictable behavior of services in concurrent environments while strictly adhering to the PSR container specification.

Differences from PHP-DI

• Only get() and has() methods exist on the container

• The factory function has completely different behavior: the closure it wraps will be called every time it is requested through get (PHP-DI exposes this as $container->make()). In PHP-DI, factory is just alternate syntax for defining a service through a closure.

• When an interface is mapped to an implementation, the default behavior is to return the configured implementation. In PHP-DI, SomeInterface::class => autowire(SomeImplementation::class) does NOT point to an explcitly-configured SomeImplementation

• A shorthand syntax for interface-to-implementation has been added

• When recursively resolving dependencies, all required parameters must also be explicitly configured (see above)

• Annotations are not supported. In future versions, @param annotations may be supported; @Inject will never be.

Design Opinions

Like many autowiring DI containers, this has some opinionated design decisions. You may or may not agree, but it's important to document them to help you make an informed choice about whether this library is right for you.

• This is based around having a distinct build/compile stage for your application's deployment process. Implicit autowiring will NOT occur in the production-ready compiled container, which yields performance improvements. Add the autowired class name to any definition file to explicitly wire it (Foo::class, is sufficient, see "Automatic autowiring" below).

• Any $id that's a valid class string should return an instance of that class (or interface, enum). As of 0.6, this is reflected in the provided type information: ->get($id) has Generic information for PHPStan where if a class-string is detected, get returns that class. This is not (currently) enforced at runtime, but be warned that e.g. $container->get(LoggerInterface::class); will be indicated as being a LoggerInteface to static analysis tools, and if the definition doesn't do that, you may get conflicts.

• All files should always be included. Do NOT skip files based on the environment. Instead, definitions should be conditional. Example:

  <?php
  
  return [
      MyInterface::class => function ($c) {
          return $c->get('use_mocks')
              ? $c->get(MyImplementationMock::class)
              : $c->get(MyImplementationReal::class);
      },
  ];

Installation

composer require firehed/container

Usage

The primary interface to the container is through the BuilderInterface.

There are two implementations:

Builder

The Builder class will create a dev container, which will determine dependencies on the fly. This is intended for use during development - reflection for autowired classes is performed on every request, which is convenient while changes are being made but adds overhead.

Compiler

The Compiler class will generate optimized code and write it to a file once, load that file, and return a container that uses the optimized code. Reflection for autowiring is only performed at compile-time, so this will run significantly faster than the dev container. However, whenever any definition changes (including constructor signatures of autowired classes), the file must be recompiled.

Tip

It is highly recommended to a) use the Compiler implementation in non-dev environments, and b) compile the container during your build process.

Running the compiler

The compilation process runs automatically the first time build() is called.

Example

<?php
declare(strict_types=1);

// Include Composer's autoloader if not already done
require 'vendor/autoload.php';

// If using a tool like dotenv, apply it here
/*
if (file_exists(__DIR__.'/.env')) {
    Dotenv\Dotenv::create(__DIR__)->load();
}
 */

$isDevMode = getenv('ENVIRONMENT') === 'development';

if ($isDevMode) {
    $builder = new Firehed\Container\Builder();
} else {
    $builder = new Firehed\Container\Compiler();
}

// Each definition file must return a definition array (see below)
foreach (glob('config/*.php') as $definitionFile) {
    $builder->addFile($definitionFile);
}

return $builder->build();

Tip

If you're following the pattern above (config files in one directory), the AutoDetect class can do this for you. See Auto-detection, below.

Definition API

All files added to the BuilderInterface must return an array. The keys of the array will map to $ids that can be checked for existence with has($id), and the values of the array will be returned when those keys are provided to get($id).

It is highly recommended that class instances use their fully-qualified class name as an array key, and to additionally create a separate interface-to-implementation mapping. The latter will happen automatically when a key is the fully-qualified name of an interface and the value is a string that maps to a class name.

Note

The library output implements a TypedContainerInterface, which adds docblock generics readable by tools like PHPStan and Psalm to PSR-11. It assumes you are following the above convention; not doing so could result in misleading output. This has no effect at runtime, and only helps during the development and CI.

Examples

The most concise examples are all part of the unit tests: tests/ValidDefinitions.

Simple values

If a scalar, array, or Enum is provided as a value, that value will be returned unmodified.

Exception: if the value is a string AND the key is the name of a declared interface, it will automatically be treated as an interface-to-implementation mapping and processed as InterfaceName::class => autowire(ImplementationName::class) When doing so, you SHOULD write the mapping with a ::class literal; e.g. \Psr\Log\LoggerInterface::class => SomeLoggerImplementation::class. This approach (as compared to strings) not only provides additional clarity when reading the file, but allows static analysis tools to detect some errors.

Objects may not be directly provided as a value and must be provided as a closure; see below. This is because the compiler cannot create an actual object instance, and thus would only work in development mode.

Closures

If a closure is provided as a value, that closure will be executed when get() is called and the value it returns will be returned. The container will be provided as the first and only parameter to the closure, so definitions may depend on other services. For services that do not have dependencies, the closure may be defined as a function that takes no parameters (a "thunk"), though at execution time the container will still be passed in (and subsequently ignored). Do not use the use() syntax to access other container definitions.

Since computed values are cached (except when wrapped with factory, see below), the closure will only be executed once regardless of how many times get() is called.

Any definition that should return an instance of an object must be defined by a closure, or using one of the helpers described below. Directly instantiating the class in the definition file is invalid.

<?php
use Psr\Container\ContainerInterface;
return [
    // This will provide a single connection to your database, deferring the
    // connection until either directly accessed or a service with PDO as a
    // dependency is accessed.
    // Note: you may opt to elide the `ContainerInterface` typehint for brevity
    PDO::class => function (ContainerInterface $c) {
        // This example assumes pdo_dsn, database_user, and database_pass are
        // defined elsewhere (probably using the `env` helper)
        return new PDO(
            $c->get('pdo_dsn'),
            $c->get('database_user'),
            $c->get('database_pass')
        );
    },
];

autowire(?string $classToAutowire = null)

Using autowire will use reflection to attempt to determine the specified class's dependencies, recursively resolve them, and return a shared instance of that object.

Required parameters must have a typehint in order to be resolved. That typehint may be to either a class or an interface; in both cases, that dependency must also be defined (but can also be autowired). Required parameters with value types (scalars, arrays, etc) are not supported and must be manually wired.

Optional parameters will always have their default value provided.

Important

Classes with any untyped constructor parameters, or those typed with int/float/bool/array, cannot be autowired.

Automatic autowiring

In the returned definition array, having a bare string value with no key will treat the value as a key to be autowired.

The following are all equivalent definitions:

<?php
/**
class MySpecialClass
{
}
class MyOtherClass
{
    public function __construct(MySpecialClass $required)
    {
        // ...
    }
}
*/
return [
    MySpecialClass::class,
    MyOtherClass::class,
];

<?php
use function Firehed\Container\autowire;
return [
    MySpecialClass::class => autowire(),
    MyOtherClass::class => autowire(),
];

<?php
use function Firehed\Container\autowire;
return [
    MySpecialClass::class => autowire(MySpecialClass::class),
    MyOtherClass::class => autowire(MyOtherClass::class),
];

<?php
return [
    MySpecialClass::class => function () {
        return new MySpecialClass();
    },
    MyOtherClass::class => function (ContainerInterface $c) {
        return new MyOtherClass($c->get(MySpecialClass::class));
    },
];

The topmost example is recommended for configuring any class that can be autowired.

factory(?closure $body = null)

Use factory to return a new copy of the class or value every time it is accessed through get()

If a paramater is not provided to the definition, the key will be used to autowire a definition. If a closure is provided, that closure will be executed instead.

env(string $variableName, ?string $default = null)

Use env to embed environment variables in your container. Like other non-factory values, these will be cached for the lifetime of the script.

env embeds a tiny DSL, allowing you to get the values set in the environment as an int, float, or bool rather than the native string read from the environment. To use this, the following methods exist:

• asBool
• asInt
• asFloat
• asEnum

These are roughly equivalent to e.g. (int) getenv('SOME_ENV_VAR'), with the exception that asBool will only allow values 0, 1, "true", and "false" (case-insensitively).

asEnum takes a class-string to a string-backed enum that you have defined, and will use ::from($envValue) to hydrate from the environment value. This does not attempt to locally normalize values, so the envvar value MUST match the backing value exactly.

Warning

Do not use getenv or $_ENV to access environment variables! If you do so, compiled containers will get the compile-time value set, which is almost certainly not the behavior you want. Instead, use the env wrapper, which will defer the access of the environment variable until the first time it is used.

If and only if you want a value compiled in, you must use getenv directly.

Source definitions like this:

<?php
use function Firehed\Container\env;
return [
    'some_key' => env('SOME_ENV_VAR'),
    'some_key_with_default' => env('SOME_ENV_VAR', 'default_value'),
    'some_key_with_null_default' => env('SOME_ENV_VAR', null),

    'some_bool' => env('SOME_BOOL')->asBool(),
    'some_int' => env('SOME_INT')->asInt(),
    'some_float' => env('SOME_FLOAT')->asFloat(),
    'some_enum' => env('SOME_ENUM')->asEnum(MyEnum::class),

    // Counterexample!
    'getenv' => getenv('VALUE_AT_COMPILE_TIME'),
];

will compile to code similar to this:

<?php
return [
    'some_key' => function () {
        $value = getenv('SOME_ENV_VAR');
        if ($value === false) {
            throw new Firehed\Container\Exceptions\EnvironmentVariableNotSet('SOME_ENV_VAR');
        }
        return $value;
    },
    'some_key_with_default' => function () {
        $value = getenv('SOME_ENV_VAR');
        if ($value === false) {
            return 'default_value';
        }
        return $value;
    },
    'some_key_with_null_default' => function () {
        $value = getenv('SOME_ENV_VAR');
        if ($value === false) {
            return null;
        }
        return $value;
    },

    'some_bool' => function () {
        $value = getenv('SOME_ENV_VAR');
        if ($value === false) {
            throw new Firehed\Container\Exceptions\EnvironmentVariableNotSet('SOME_ENV_VAR');
        }
        $value = strtolower($value);
        if ($value === '1' || $value === 'true') {
            return true;
        } elseif ($value === '0' || $value === 'false') {
            return false;
        } else {
            throw new OutOfBoundsException('Invalid boolean value');
        }
    },
    'some_int' => function () {
        $value = getenv('SOME_INT');
        if ($value === false) {
            throw new Firehed\Container\Exceptions\EnvironmentVariableNotSet('SOME_INT');
        }
        return (int)$value;
    },
    'some_float' => function () {
        $value = getenv('SOME_FLOAT');
        if ($value === false) {
            throw new Firehed\Container\Exceptions\EnvironmentVariableNotSet('SOME_FLOAT');
        }
        return (float)$value;
    },
    'some_enum' => function () {
        $value = getenv('SOME_ENUM');
        if ($value === false) {
            throw new Firehed\Container\Exceptions\EnvironmentVariableNotSet('SOME_ENUM');
        }
        return MyEnum::from($value);
    },

    // Counterexample!
    'getenv' => 'whatever_value_is_in_your_current_environment',
];

Auto-detection

If your software is following common conventions, the container bootstrapping can be greatly simplified:

$container = \Firehed\Container\AutoDetect::from('config');

It will auto-detect your environment, looking at ENVIRONMENT or ENV environment variables, in that order. If it's any of local, dev, or development (case-insensitive), then it will use the dev container, which is not cached or compiled. Any other value will run the compilation process, writing the output to AutoDetect::$compiledOutputPath = 'vendor/compiledConfig.php'. You may change the output directory by changing that variable (be mindful of getcwd()!); the default writes into Composer's vendor directory since it's commonly gitignored.