`SyncLists` are array based lists similar to C# [List\<T\>](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.list-1?view=netframework-4.7.2) that synchronize their contents from the server to the clients.
* In HLAPI, SyncLists were synchornized immediatelly when they changed. If you add 10 elements, that means 10 separate messages. Mirror synchronizes synclists with the syncvars. The 10 elements and other syncvars are batched together into a single message. Mirror also respects the sync interval when synchronizing lists.
* In HLAPI the Callback tells you the operation and index. In Mirror, the callback also receives an item. We made this change so that we could tell what item was removed.
Create a class that derives from SyncList<T> for your specific type. This is necesary because Mirror will add methods to that class with the weaver. Then add a SyncList field to your NetworkBehaviour class. For example:
You can also detect when a synclist changes in the client or server. This is useful for refreshing your character when you add equipment or determining when you need to update your database. Subscribe to the Callback event typically during `Start`, `OnClientStart` or `OnServerStart` for that. Note that by the time you subscribe, the list will already be initialized, so you will not get a call for the initial data, only updates.
```cs
class Player : NetworkBehaviour {
SyncListItem inventory;
// this will add the delegates on both server and client.
// Use OnStartClient instead if you just want the client to act upon updates
By default, `SyncList` uses a `List` to store it's data. If you want to use a different list implementation, add a constructor and pass the list implementation to the parent constructor. For example:
```cs
class SyncListItem : SyncList<Item>
{
public SyncListItem() : base(new MyIList<Item>()) {}