Building a Service Container in PHP

A service container builds dependencies and injects interfaces into application components.

What It Does

A service container builds dependencies and injects interfaces into application components. The following examples distinguish a normal use case, a boundary case and a practical application.

Requirements and Compatibility

PHP 8.x and a local test environment. Apply input validation, correct error handling and the requirements of any optional libraries.

The code focuses on the core concept. Production implementation may also need routes, validation, persistence, authorization or deployment tooling.

Example 1: Basic Behavior

Understand the primary operation and its inputs.

<?php
interface Exporter { public function type(): string; }
class CsvExporter implements Exporter { public function type(): string { return 'csv'; } }
function exporter(string $format): Exporter { return match ($format) { 'csv' => new CsvExporter(), default => throw new InvalidArgumentException('Unknown format') }; }
echo exporter('csv')->type();

Example 2: Another Case

Check failure behavior or a different execution path.

<?php
class CacheService { public function __construct(public string $name) {} }
$container = ['cache' => fn () => new CacheService('local')];
$cache = $container['cache']();
echo $cache->name;

Practical Example: Putting It to Use

A small container resolves dependencies using explicitly registered factories.

<?php
final class Resolver { private array $services = []; public function set(string $id, Closure $factory): void { $this->services[$id] = $factory; } public function get(string $id): mixed { return ($this->services[$id] ?? throw new RuntimeException('Unknown service'))(); } }
$r = new Resolver(); $r->set('clock', fn () => new DateTimeImmutable('2026-01-01'));
echo $r->get('clock')->format('Y');

Important Behavior and Edge Cases

Containers should describe object construction, not become an unrestricted global variable accessed everywhere.

Comparison with Related Functions or Approaches

Common Beginner Mistakes

Key Takeaways

• A service container builds dependencies and injects interfaces into application components.
• Containers should describe object construction, not become an unrestricted global variable accessed everywhere.
• Constructor injection is often simpler for small applications.

Before adapting these examples, verify the return values, test the failure paths and confirm that your application meets its security and environment requirements.