# Services¶

## Characteristica¶

• Services MUST be used as objects, they are never static
• A single service MUST consist of one class only
• Services MUST be located in a Service/ directory and MUST end with Service, eg. Service/FoobarService.php
• Service instances MAY hold state, but SHOULD be stateless
• Services MAY use configuration, but SHOULD not
• Services MAY have multiple entry points, but SHOULD have only one
• Services SHOULD NOT be singletons

## Rationale¶

A “service” in this context is meant as the relatively short-sighted process of putting a class into a Service/ subfolder and calling it a WhateverService. It does not have too much to do with the DDD Service context, which is broader. This section is just about which scope can be expected for classes residing in a Service folder within Core extensions.

From this point of view, services in TYPO3 world are a relatively slim class construct that encapsulates a specific concern. It is too big for a small static method, it may hold state, but it is still just a relatively small scope. Each service consists typically of only a single class. A bigger construct with interfaces, multiple sub classes is not called a service anymore.

The above MAY and SHOULD mean that a single service MAY do a single one or two of them, but if for instance a service is relatively big, has many entry points, keeps state and depends on configuration, this is too much and is a sign it should be modeled in a different and more dedicated and more disjoint way.

The main risk with service classes is that they pile up to a conglomeration of helper stuff classes that are hanging around without good motivation. It is important that a service class should not be a bin for something that just does not fit to a different better place within the scope of a specific extension.

## Good Examples¶

• \TYPO3\CMS\Extbase\Service\CacheService
• Small and straight scope with useful helpers
• It is a singleton, but that is feasible in this case

• \TYPO3\CMS\Core\Service\AbstractService,
• Not modeled in a sane way, this should be within Core/Authentication