docs/guide/csharp/xlang-serialization.md

---
title: Xlang Serialization
sidebar_position: 3
id: xlang_serialization
license: |
  Licensed to the Apache Software Foundation (ASF) under one or more
  contributor license agreements.  See the NOTICE file distributed with
  this work for additional information regarding copyright ownership.
  The ASF licenses this file to You under the Apache License, Version 2.0
  (the "License"); you may not use this file except in compliance with
  the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
---

Apache Fory™ C# supports xlang serialization with other Fory implementations.

## Xlang Fory Instance

C# always writes and reads the xlang frame header. There is no mode switch, so interoperability code
only needs to configure the remaining settings such as compatibility mode and reference
tracking.

```csharp
Fory fory = Fory.Builder()
    .Build();
```

## Register with Stable IDs

```csharp
[ForyStruct]
public sealed class Person
{
    public string Name { get; set; } = string.Empty;
    public int Age { get; set; }
}

Fory fory = Fory.Builder()
    .Build();

fory.Register<Person>(100);
```

Use the same ID mapping on all languages.

## Register by Name

```csharp
fory.Register<Person>("com.example.Person");
```

## Xlang Example

### C# (Serializer)

```csharp
Person person = new() { Name = "Alice", Age = 30 };
byte[] payload = fory.Serialize(person);
```

### Java (Deserializer)

```java
Fory fory = Fory.builder()
        .withXlang(true)
        .withRefTracking(true)
    .build();

fory.register(Person.class, 100);
Person value = (Person) fory.deserialize(payloadFromCSharp);
```

### Python (Deserializer)

```python
import pyfory

fory = pyfory.Fory(xlang=True, ref=True)
fory.register_type(Person, type_id=100)
value = fory.deserialize(payload_from_csharp)
```

## Type Mapping Reference

See [xlang guide](../xlang/index.md) for complete mapping.

For reduced-precision numeric payloads, use `Half` / `Half[]` or `List<Half>` for xlang `float16`, and `BFloat16` / `BFloat16[]` or `List<BFloat16>` for xlang `bfloat16`.

## Lists and Dense Arrays

C# `List<T>` maps to Fory `list<T>`. Use the schema marker
`Apache.Fory.Schema.Types.Array<T>` when a field is dense `array<T>`.

| Fory schema       | C# schema marker sketch |
| ----------------- | ----------------------- |
| `list<int32>`     | `S.List<S.Int32>`       |
| `array<bool>`     | `S.Array<S.Bool>`       |
| `array<int8>`     | `S.Array<S.Int8>`       |
| `array<int16>`    | `S.Array<S.Int16>`      |
| `array<int32>`    | `S.Array<S.Int32>`      |
| `array<int64>`    | `S.Array<S.Int64>`      |
| `array<uint8>`    | `S.Array<S.UInt8>`      |
| `array<uint16>`   | `S.Array<S.UInt16>`     |
| `array<uint32>`   | `S.Array<S.UInt32>`     |
| `array<uint64>`   | `S.Array<S.UInt64>`     |
| `array<float16>`  | `S.Array<S.Float16>`    |
| `array<bfloat16>` | `S.Array<S.BFloat16>`   |
| `array<float32>`  | `S.Array<S.Float32>`    |
| `array<float64>`  | `S.Array<S.Float64>`    |

## Best Practices

1. Keep type IDs stable and documented.
2. Keep compatible mode enabled for rolling upgrades.
3. Register all user types on both read/write peers.
4. Validate integration with real payload round trips.

## Related Topics

- [Type Registration](type-registration.md)
- [Schema Evolution](schema-evolution.md)
- [Supported Types](supported-types.md)