add IEquatable<SDate> interface to SDate (#307)

src/StardewModdingAPI/Utilities/SDate.cs

@@ -5,7 +5,7 @@ using StardewValley;
 namespace StardewModdingAPI.Utilities
 {
     /// <summary>Represents a Stardew Valley date.</summary>
-    public class SDate
+    public class SDate : IEquatable<SDate>
     {
         /*********
         ** Properties
@@ -66,6 +66,12 @@ namespace StardewModdingAPI.Utilities
             this.Year = year;
         }
 
+        /// <summary>Get the current in-game date.</summary>
+        public static SDate Now()
+        {
+            return new SDate(Game1.dayOfMonth, Game1.currentSeason, Game1.year);
+        }
+
         /// <summary>Get a new date with the given number of days added.</summary>
         /// <param name="offset">The number of days to add.</param>
         /// <returns>Returns the resulting date.</returns>
@@ -108,15 +114,37 @@ namespace StardewModdingAPI.Utilities
             return $"{this.Day:00} {this.Season} Y{this.Year}";
         }
 
-        /// <summary>Get the current in-game date.</summary>
-        public static SDate Now()
+        /****
+        ** IEquatable
+        ****/
+        /// <summary>Get whether this instance is equal to another.</summary>
+        /// <param name="other">The other value to compare.</param>
+        public bool Equals(SDate other)
         {
-            return new SDate(Game1.dayOfMonth, Game1.currentSeason, Game1.year);
+            return this == other;
         }
 
-        /*********
-        ** Operator methods
-        *********/
+        /// <summary>Get whether this instance is equal to another.</summary>
+        /// <param name="obj">The other value to compare.</param>
+        public override bool Equals(object obj)
+        {
+            return obj is SDate other && this == other;
+        }
+
+        /// <summary>Get a hash code which uniquely identifies a date.</summary>
+        public override int GetHashCode()
+        {
+            // return the number of days since 01 spring Y1
+            int yearIndex = this.Year - 1;
+            return
+                yearIndex * this.DaysInSeason * this.SeasonsInYear
+                + this.GetSeasonIndex() * this.DaysInSeason
+                + this.Day;
+        }
+
+        /****
+        ** Operators
+        ****/
         /// <summary>Get whether one date is equal to another.</summary>
         /// <param name="date">The base date to compare.</param>
         /// <param name="other">The other date to compare.</param>
@@ -166,25 +194,6 @@ namespace StardewModdingAPI.Utilities
             return date?.GetHashCode() < other?.GetHashCode();
         }
 
-        /// <summary>Overrides the equals function.</summary>
-        /// <param name="obj">Object being compared.</param>
-        /// <returns>The equalaity of the object.</returns>
-        public override bool Equals(object obj)
-        {
-            return obj is SDate other && this == other;
-        }
-
-        /// <summary>Get a hash code which uniquely identifies a date.</summary>
-        public override int GetHashCode()
-        {
-            // return the number of days since 01 spring Y1
-            int yearIndex = this.Year - 1;
-            return
-                yearIndex * this.DaysInSeason * this.SeasonsInYear
-                + this.GetSeasonIndex() * this.DaysInSeason
-                + this.Day;
-        }
-
 
         /*********
         ** Private methods