create watcher core (#310)

2 files changed, 39 insertions, 0 deletions

diff --git a/src/SMAPI/Framework/StateTracking/Comparers/GenericEqualsComparer.cs b/src/SMAPI/Framework/StateTracking/Comparers/GenericEqualsComparer.cs
new file mode 100644
index 00000000..cc1d6553
--- /dev/null
+++ b/src/SMAPI/Framework/StateTracking/Comparers/GenericEqualsComparer.cs
@@ -0,0 +1,31 @@
+using System.Collections.Generic;
+using System.Runtime.CompilerServices;
+
+namespace StardewModdingAPI.Framework.StateTracking.Comparers
+{
+    /// <summary>Compares values using their <see cref="object.Equals(object)"/> method. This should only be used when <see cref="EquatableComparer{T}"/> won't work, since this doesn't validate whether they're comparable.</summary>
+    /// <typeparam name="T">The value type.</typeparam>
+    internal class GenericEqualsComparer<T> : IEqualityComparer<T>
+    {
+        /*********
+        ** Public methods
+        *********/
+        /// <summary>Determines whether the specified objects are equal.</summary>
+        /// <returns>true if the specified objects are equal; otherwise, false.</returns>
+        /// <param name="x">The first object to compare.</param>
+        /// <param name="y">The second object to compare.</param>
+        public bool Equals(T x, T y)
+        {
+            if (x == null)
+                return y == null;
+            return x.Equals(y);
+        }
+
+        /// <summary>Get a hash code for the specified object.</summary>
+        /// <param name="obj">The value.</param>
+        public int GetHashCode(T obj)
+        {
+            return RuntimeHelpers.GetHashCode(obj);
+        }
+    }
+}
diff --git a/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs b/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
index 4f1ac9f4..d7a02668 100644
--- a/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
+++ b/src/SMAPI/Framework/StateTracking/FieldWatchers/WatcherFactory.cs
@@ -12,6 +12,14 @@ namespace StardewModdingAPI.Framework.StateTracking.FieldWatchers
         /*********
         ** Public methods
         *********/
+        /// <summary>Get a watcher which compares values using their <see cref="object.Equals(object)"/> method. This method should only be used when <see cref="ForEquatable{T}"/> won't work, since this doesn't validate whether they're comparable.</summary>
+        /// <typeparam name="T">The value type.</typeparam>
+        /// <param name="getValue">Get the current value.</param>
+        public static ComparableWatcher<T> ForGenericEquality<T>(Func<T> getValue) where T : struct
+        {
+            return new ComparableWatcher<T>(getValue, new GenericEqualsComparer<T>());
+        }
+
         /// <summary>Get a watcher for an <see cref="IEquatable{T}"/> value.</summary>
         /// <typeparam name="T">The value type.</typeparam>
         /// <param name="getValue">Get the current value.</param>