Add init-only properties to rule

docs/fundamentals/code-analysis/quality-rules/ca2227.md

@@ -1,7 +1,7 @@
 ---
 title: "CA2227: Collection properties should be read only (code analysis)"
 description: "Learn about code analysis rule CA2227: Collection properties should be read only"
-ms.date: 09/28/2018
+ms.date: 07/08/2021
 ms.topic: reference
 f1_keywords:
 - CA2227
@@ -29,13 +29,13 @@ An externally visible, writable property is of a type that implements <xref:Syst
 
 ## Rule description
 
-A writable collection property allows a user to replace the collection with a completely different collection. A read-only property stops the collection from being replaced, but still allows the individual members to be set. If replacing the collection is a goal, the preferred design pattern is to include a method to remove all the elements from the collection, and a method to repopulate the collection. See the <xref:System.Collections.ArrayList.Clear%2A> and <xref:System.Collections.ArrayList.AddRange%2A> methods of the <xref:System.Collections.ArrayList?displayProperty=fullName> class for an example of this pattern.
+A writable collection property allows a user to replace the collection with a completely different collection. A read-only or [init-only](../../../csharp/language-reference/keywords/init.md) property stops the collection from being replaced, but still allows the individual members to be set. If replacing the collection is a goal, the preferred design pattern is to include a method to remove all the elements from the collection, and a method to repopulate the collection. See the <xref:System.Collections.ArrayList.Clear%2A> and <xref:System.Collections.ArrayList.AddRange%2A> methods of the <xref:System.Collections.ArrayList?displayProperty=fullName> class for an example of this pattern.
 
 Both binary and XML serialization support read-only properties that are collections. The <xref:System.Xml.Serialization.XmlSerializer?displayProperty=fullName> class has specific requirements for types that implement <xref:System.Collections.ICollection> and <xref:System.Collections.IEnumerable?displayProperty=fullName> in order to be serializable.
 
 ## How to fix violations
 
-To fix a violation of this rule, make the property read-only. If the design requires it, add methods to clear and repopulate the collection.
+To fix a violation of this rule, make the property read-only or [init-only](../../../csharp/language-reference/keywords/init.md). If the design requires it, add methods to clear and repopulate the collection.
 
 ## When to suppress warnings
 
@@ -54,3 +54,7 @@ The following example shows a type with a writable collection property and shows
 ## Related rules
 
 - [CA1819: Properties should not return arrays](ca1819.md)
+
+## See also
+
+- [Properties in C#](../../../csharp/programming-guide/classes-and-structs/properties.md)

docs/fundamentals/code-analysis/quality-rules/snippets/csharp/all-rules/ca2227.cs

@@ -11,7 +11,7 @@ public ArrayList SomeStrings
             get;
 
             // This set accessor violates rule CA2227.
-            // To fix the code, remove this set accessor.
+            // To fix the code, remove this set accessor or change it to init.
             set;
         }