Remove ILive<> interface (and use abstract Live<> instead)

osu.Game/Database/Live.cs

@@ -0,0 +1,59 @@
+// Copyright (c) ppy Pty Ltd <contact@ppy.sh>. Licensed under the MIT Licence.
+// See the LICENCE file in the repository root for full licence text.
+
+using System;
+
+#nullable enable
+
+namespace osu.Game.Database
+{
+    /// <summary>
+    /// A wrapper to provide access to database backed classes in a thread-safe manner.
+    /// </summary>
+    /// <typeparam name="T">The databased type.</typeparam>
+    public abstract class Live<T> : IEquatable<Live<T>>
+        where T : class, IHasGuidPrimaryKey
+    {
+        public Guid ID { get; }
+
+        /// <summary>
+        /// Perform a read operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        public abstract void PerformRead(Action<T> perform);
+
+        /// <summary>
+        /// Perform a read operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        public abstract TReturn PerformRead<TReturn>(Func<T, TReturn> perform);
+
+        /// <summary>
+        /// Perform a write operation on this live object.
+        /// </summary>
+        /// <param name="perform">The action to perform.</param>
+        public abstract void PerformWrite(Action<T> perform);
+
+        /// <summary>
+        /// Whether this instance is tracking data which is managed by the database backing.
+        /// </summary>
+        public abstract bool IsManaged { get; }
+
+        /// <summary>
+        /// Resolve the value of this instance on the update thread.
+        /// </summary>
+        /// <remarks>
+        /// After resolving, the data should not be passed between threads.
+        /// </remarks>
+        public abstract T Value { get; }
+
+        protected Live(Guid id)
+        {
+            ID = id;
+        }
+
+        public bool Equals(Live<T>? other) => ID == other?.ID;
+
+        public override string ToString() => PerformRead(i => i.ToString());
+    }
+}