Modify S2328: Exclude value types (#3670)

rules/S2328/csharp/rule.adoc

@@ -1,18 +1,25 @@
 == Why is this an issue?
 
-``++GetHashCode++`` is used to file an object in a ``++Dictionary++`` or ``++Hashtable++``. If ``++GetHashCode++`` uses non-``++readonly++`` fields and those fields change after the object is stored, the object immediately becomes mis-filed in the ``++Hashtable++``. Any subsequent test to see if the object is in the ``++Hashtable++`` will return a false negative.
+`GetHashCode` is used to file an object in a `Dictionary` or `Hashtable`. If `GetHashCode` uses non-`readonly` fields and those fields change after the object is stored, the object immediately becomes mis-filed in the `Hashtable`. Any subsequent test to see if the object is in the `Hashtable` will return a false negative.
 
+=== Exceptions
 
-=== Noncompliant code example
+This rule does not raise if the type implementing `GetHashCode` is a value type, for example a `struct` or a `record struct`, since when a value type is stored in a `Dictionary` or `Hashtable`, a copy of the value is stored, not a reference to the value.
 
-[source,csharp]
+== How to fix it
+
+=== Code examples
+
+==== Noncompliant code example
+
+[source,csharp,diff-id=1,diff-type=noncompliant]
 ----
-public class Person 
+public class Person
 {
   public int age;
   public string name;
 
-  public override int GetHashCode() 
+  public override int GetHashCode()
   {
     int hash = 12;
     hash += this.age.GetHashCode(); // Noncompliant
@@ -22,16 +29,16 @@ public class Person
 ----
 
 
-=== Compliant solution
+==== Compliant solution
 
-[source,csharp]
+[source,csharp,diff-id=1,diff-type=compliant]
 ----
-public class Person 
+public class Person
 {
   public readonly DateTime birthday;
   public string name;
 
-  public override int GetHashCode() 
+  public override int GetHashCode()
   {
     int hash = 12;
     hash += this.birthday.GetHashCode();