How about a NetworkBehaviourReference<T>?

It would be amazing if RPC arguments could just actually be any NetworkBehaviour derivative class instead of only NetworkBehaviourReference so that the compiler could enforce type on those RPC arguments instead of boilerplate cast / TryGet code.

Short of that, doing an RPC with NetworkBehaviourReference<MyNetworkBehaviourClass> at least gives me peace of mind that the compiler can catch me trying to pass the RPC a reference to a NetworkBehaviour that isn't a MyNetworkBehaviourClass.

I did it like this:

using System;
using System.Runtime.CompilerServices;

namespace Unity.Netcode
{
    public struct NetworkBehaviourReference<T> : INetworkSerializable, IEquatable<NetworkBehaviourReference<T>>
        where T : NetworkBehaviour
    {
        private NetworkObjectReference m_NetworkObjectReference;
        private ushort m_NetworkBehaviourId;

        public NetworkBehaviourReference(NetworkBehaviour networkBehaviour)
        {
            if (networkBehaviour == null)
            {
                m_NetworkObjectReference = new NetworkObjectReference((NetworkObject)null);
                m_NetworkBehaviourId = 0;
                return;
                // throw new ArgumentNullException(nameof(networkBehaviour));
            }
            if (networkBehaviour.NetworkObject == null)
            {
                throw new ArgumentException($"Cannot create {nameof(NetworkBehaviourReference<T>)} from {nameof(NetworkBehaviour)} without a {nameof(NetworkObject)}.");
            }

            m_NetworkObjectReference = networkBehaviour.NetworkObject;
            m_NetworkBehaviourId = networkBehaviour.NetworkBehaviourId;
        }

        public bool TryGet(out T networkBehaviourSubtype, NetworkManager networkManager = null)
        {
            networkBehaviourSubtype = GetInternal(this, null) as T;
            return networkBehaviourSubtype != null;
        }

        [MethodImpl(MethodImplOptions.AggressiveInlining)]
        private static NetworkBehaviour GetInternal(NetworkBehaviourReference<T> networkBehaviourRef, NetworkManager networkManager = null)
        {
            if (networkBehaviourRef.m_NetworkObjectReference.TryGet(out NetworkObject networkObject, networkManager))
            {
                return networkObject.GetNetworkBehaviourAtOrderIndex(networkBehaviourRef.m_NetworkBehaviourId);
            }

            return null;
        }

        public bool Equals(NetworkBehaviourReference<T> other)
        {
            return m_NetworkObjectReference.Equals(other.m_NetworkObjectReference) && m_NetworkBehaviourId == other.m_NetworkBehaviourId;
        }

        public override bool Equals(object obj)
        {
            return obj is NetworkBehaviourReference<T> other && Equals(other);
        }

        public override int GetHashCode()
        {
            unchecked
            {
                return (m_NetworkObjectReference.GetHashCode() * 397) ^ m_NetworkBehaviourId.GetHashCode();
            }
        }

        public void NetworkSerialize<T>(BufferSerializer<T> serializer) where T : IReaderWriter
        {
            m_NetworkObjectReference.NetworkSerialize(serializer);
            serializer.SerializeValue(ref m_NetworkBehaviourId);
        }

        public static implicit operator T(NetworkBehaviourReference<T> networkBehaviourRef) => GetInternal(networkBehaviourRef) as T;

        public static implicit operator NetworkBehaviourReference<T>(T networkBehaviourSubtype) => new NetworkBehaviourReference<T>(networkBehaviourSubtype);
    }
}

首先檢查 NetworkBehaviourReference、NetworkObjectReference，以及 issue 中描述的 RPC 引數處理。判斷泛型 NetworkBehaviour 參照或直接型別化的 RPC 引數是否符合現有的序列化與 lookup 路徑；完成的標準是強制使用型別化參照，並且不需要目前的 cast 或 TryGet boilerplate 即可解析，同時加入適當的覆蓋測試。