Reflection-Based Autowiring

Overview

Reflection-based autowiring is a core feature of the DomainFlow Container that leverages PHP’s Reflection API to automatically resolve and inject dependencies. By inspecting constructor parameters and type hints, the container can instantiate classes without the need for explicit dependency declarations. This reduces boilerplate code and streamlines the dependency injection process.

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Key Concepts

Automatic Dependency Resolution:

The container examines the constructor of a class, reads the type hints, and automatically determines which dependencies to inject.

Handling Advanced Types:

The autowiring mechanism supports:

• Named Types: Automatically resolves dependencies based on their type hints.
• Union and Intersection Types: Uses dedicated methods to handle complex type declarations, applying priority rules for union types and ensuring all constraints are met for intersection types.

Error Handling:

If a dependency cannot be resolved (for example, a built-in type without a default value), the container throws a clear exception to alert you during development.

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Implementation Details

The autowiring functionality includes two key aspects:

Building Instances:

The build() method utilizes reflection to instantiate classes while automatically resolving their constructor dependencies.

Parameter Resolution:

The resolveParameter() method examines each constructor parameter’s type and determines the appropriate dependency to inject. For more complex scenarios:

• Union Types: The resolveUnionType() method attempts each type in a defined order.
• Intersection Types: The resolveIntersectionType() method ensures that all required type constraints are satisfied.

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Parameter Resolution Methods

Method	Signature	Description
build	build(string $concrete, array $parameters = []): mixed	Instantiates a class by resolving its constructor dependencies.
resolveParameter	resolveParameter(ReflectionParameter $param, array $parameters, string $parentClass): mixed	Resolves a single constructor parameter based on type hints and default values.

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Example Usage

Consider a scenario with a UserService that depends on an EmailService and a configuration array:

class EmailService {
    public function send($recipient, $message) {
        // Email sending logic...
    }
}

class UserService {
    public function __construct(EmailService $emailService, array $config) {
        $this->emailService = $emailService;
        $this->config = $config;
    }
}

// Create the container and optionally bind configuration defaults.
$container = new Container();

// Bind a configuration array for demonstration purposes.
$container->bind('config', function() {
    return ['smtp_host' => 'smtp.example.com'];
});

// Resolve UserService. The container uses reflection to automatically:
// - Instantiate EmailService and inject it.
// - Retrieve the configuration via the binding for 'config'.
$userService = $container->get(UserService::class);

In this example:

• The container inspects UserService's constructor and automatically resolves an instance of EmailService.
• It injects the configuration array (bound as 'config') into the second parameter.
• No manual wiring is required as autowiring handles dependency resolution automatically.

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Benefits

• Reduced Boilerplate:
  Developers no longer need to manually specify every dependency in the container’s configuration.

• Ease of Maintenance:
  Changes to class constructors are automatically managed, provided type hints remain consistent.

• Robust Type Handling:
  Advanced support for union and intersection types ensures that even complex dependencies are resolved correctly.

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Summary

Reflection-based autowiring simplifies dependency injection by leveraging PHP’s Reflection API to automatically inspect and resolve dependencies. This feature minimizes manual configuration, reduces boilerplate code, and improves maintainability by ensuring that dependencies are managed automatically. It is a fundamental aspect of the DomainFlow Container, making it easier to build modular and scalable applications.