> For the complete documentation index, see [llms.txt](https://php-fhir-tools.ardenexal.net/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://php-fhir-tools.ardenexal.net/serialization/ig-aware.md).

# Serializing IG Extensions & Profiles

When you generate typed classes for an [Implementation Guide](/code-generation/implementation-guides.md), the serializer must be IG-aware to deserialize those typed extensions and profile subclasses into their PHP classes (rather than the base `Extension` type). Build the service with `createWithIG()`, pointing it at your generated IG output directory and its PSR-4 namespace:

```php
<?php

use Ardenexal\FHIRTools\Component\Serialization\FHIRSerializationService;
use Ardenexal\FHIRTools\Component\Serialization\FhirVersion;

$serializer = FHIRSerializationService::createWithIG(
    igOutputDirectory: '/app/src/FHIRIG',
    igNamespace: 'App\\FHIR\\IG',
    version: FhirVersion::R4B,
);
```

`createWithIG()` scans the base model `Extension` directories plus the optional IG output directory, building an IG type registry. The registry deserializes typed extensions into their PHP classes, resolves `meta.profile` URLs to their profile classes, and picks the right class for a sliced element using the discriminator (the field an IG names to tell sliced entries apart).

{% hint style="info" %}
With no IG arguments, `createWithIG()` (and therefore `createDefault()`, which delegates to it) still registers the base model extensions, so standard typed extensions resolve out of the box. Pass an empty string for `igOutputDirectory` / `igNamespace` to skip IG scanning.
{% endhint %}

The signature is:

```php
public static function createWithIG(
    string $igOutputDirectory = '',
    string $igNamespace = '',
    FhirVersion $version = FhirVersion::R4
): self
```

See the [FHIRBundle guide](/symfony-bundle/configuration.md) for generating IG classes with `fhir:generate-ig`.


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