Clarifying GetHashCode for collections

README.md

@@ -113,11 +113,22 @@ public record struct Test(IReadOnlyList<int> Numbers)
 }
 ```
 
-It is not necessary for records to implement `IEquatable<T>`. When you write your implementations `SequenceEqual` is very useful for comparing  collections, eg:
+It is not necessary for records to implement `IEquatable<T>`. When you write your implementations `SequenceEqual` is very useful for comparing  collections.
+
+Note that GetHashCode for collections is tricky!
 
 ```
-public readonly bool Equals(Test other) => Numbers.SequenceEqual(other.Numbers);
-public override readonly int GetHashCode() => Numbers.GetHashCode();
+public override int GetHashCode() => Numbers.GetHashCode(); // BROKEN!
+public override int GetHashCode() => HashCode.Combine(Numbers); // BROKEN!
+
+public override int GetHashCode() // CORRECT IMPLEMENTATION
+{
+	var hash = new HashCode();
+	foreach (var n in Numbers) hash.Add(n);
+	return hash.ToHashCode();
+}
+
+public readonly bool Equals(Test other) => Numbers.SequenceEqual(other.Numbers); // CORRECT IMPLEMENTATION
 ```
 
 ## Testing