# Utilities & Extensions

**DOTSNET** comes with a few usability extensions for ECS, found in Extensions.cs:

#### `Entity.UniqueId()`

On the server we need to store spawned entities by their unique ids.

We added a simple `Entity.UniqueId()` extension for that. The id is created from the two Entity struct fields: Index & Version, and is guaranteed to be unique as long as the program runs.<br>

#### `DynamicBuffer.Contains(value)`

`DynamicBuffer` doesn’t come with a Contains helper function, and adding one can be cumbersome since there are a few things to consider for Burst support, so **DOTSNET** comes with one to make life easier.

*Note that while it’s not necessary, for maximum performance it’s recommended to implement `GetHashCode()` in your `IBufferElementData` structs so that `DynamicBuffer.Contains` doesn’t default to using Reflection for `GetHashCode`.*<br>

#### `NativeMultiMap.TryIterate(key, out value, ref iterator)`

Iterating a `NativeMultiMap` is cumbersome because we need to call both `TryGetFirstValue` and `TryGetNextValue`:

```csharp
if (messages.TryGetFirstValue(connectionId, out message,
    out NativeMultiHashMapIterator<int> it))
{
    Send(message, connectionId);
    while (messages.TryGetNextValue(out message, ref it))
    {
        Send(message, connectionId);
    }
}
```

The problem with this syntax is that it requires redundant follow-up code. Notice how Send() needs to be in there twice.<br>

Instead, **DOTSNET** provides a `TryIterate` helper function:

```csharp
NativeMultiHashMapIterator<T>? iterator = default;
while (messages.TryIterate(connectionId, out message, ref iterator))
{
    Send(message, connectionId);
}
```

This way we don’t need redundant follow-up code. `Send` is only called once.

{% hint style="info" %}
**Note:** don’t forget the “?” when declaring your iterator type.
{% endhint %}