> For the complete documentation index, see [llms.txt](https://quantumphp.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://quantumphp.gitbook.io/docs/packages/service/contracts.md).

# Contracts

This page describes the behaviors you can rely on when integrating with the Service package.

## Service type contract

Use subclasses of `Quantum\Service\Service` as service targets.

```php
use Quantum\Service\Service;

class ReportService extends Service
{
}
```

Non-service classes are rejected before resolution.

## Resolution modes

### `ServiceFactory::create(string $serviceClass, array $args = [])`

Contract:

* validates service class eligibility
* returns a fresh instance
* accepts runtime constructor arguments

### `ServiceFactory::get(string $serviceClass, array $args = [])`

Contract:

* validates service class eligibility
* registers the service class with DI when needed
* returns the shared instance for that service class
* applies runtime constructor arguments when the shared instance is created
* reuses the same shared instance on later calls for the same service class

## Helper contract

```php
service(string $serviceClass, bool $singleton = false): Service
```

Behavior:

* `false` resolves a fresh instance
* `true` resolves the shared instance
* helper does not accept constructor args

If you need runtime args, use `ServiceFactory::create()` or `ServiceFactory::get()`. For shared services, pass those args on the first `get()` call that creates the instance.

## Undefined method contract

Undefined method calls throw immediately.

Practical effect: service method typos surface immediately instead of being silently ignored.

## Exception cases to handle

* service class does not exist
* class exists but does not extend `Quantum\Service\Service`
* constructor dependencies do not resolve through DI or provided args
* undefined service method is called


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