`SyncHashSet` are sets similar to C# [HashSet\<T\>](https://docs.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1) that synchronize their contents from the server to the clients.
A SyncHashSet can contain items of the following types:
- Basic type (byte, int, float, string, UInt64, etc)
- Built-in Unity math type (Vector3, Quaternion, etc)
- NetworkIdentity
- GameObject with a NetworkIdentity component attached.
- Structure with any of the above
## Usage
Create a class that derives from SyncHashSet<T> for your specific type. This is necesary because Mirror will add methods to that class with the weaver. Then add a SyncHashSet field to your NetworkBehaviour class. For example:
```cs
class Player : NetworkBehaviour {
class SyncSkillSet : SyncHashSet<string> {}
SyncSkillSet skills = new SyncSkillSet();
int skillPoints = 10;
[Command]
public void CmdLearnSkill(string skillName)
{
if (skillPoints > 1)
{
skillPoints--;
skills.Add(skillName);
}
}
}
```
You can also detect when a SyncHashSet changes. This is useful for refreshing your character in the client 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 set will already be initialized, so you will not get a call for the initial data, only updates.
```cs
class Player : NetworkBehaviour
{
class SyncSetBuffs : SyncHashSet<string> {};
SyncSetBuffs buffs = new SyncSetBuffs();
// this will add the delegate on the client.
// Use OnStartServer instead if you want it on the server
