add AsReadonly for IList and IDictionary (#150)

Author: SimonCropp

api_list.include.md

@@ -20,6 +20,11 @@
  * `Boolean TryGetValue<T>(T, T&)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1.trygetvalue)
 
 
+#### IDictionary<TKey,TValue>
+
+ * `Collections.ObjectModel.ReadOnlyDictionary<TKey,TValue> AsReadOnly<TKey, TValue>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-2(system-collections-generic-idictionary((-0-1))))
+
+
 #### IEnumerable<TSource>
 
  * `IEnumerable<KeyValuePair<TKey,TAccumulate>> AggregateBy<TSource, TKey, TAccumulate>(Func<TSource,TKey>, TAccumulate, Func<TAccumulate,TSource,TAccumulate>, IEqualityComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.aggregateby#system-linq-enumerable-aggregateby-3(system-collections-generic-ienumerable((-0))-system-func((-0-1))-system-func((-1-2))-system-func((-2-0-2))-system-collections-generic-iequalitycomparer((-1))))
@@ -35,6 +40,11 @@
  * `HashSet<TSource> ToHashSet<TSource>(IEqualityComparer<TSource>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.tohashset#system-linq-enumerable-tohashset-1(system-collections-generic-ienumerable((-0))-system-collections-generic-iequalitycomparer((-0))))
 
 
+#### IList<T>
+
+ * `Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly<T>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-1(system-collections-generic-ilist((-0))))
+
+
 #### IReadOnlyDictionary<TKey,TValue>
 
  * `TValue GetValueOrDefault<TKey, TValue>(TKey)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.getvalueordefault)

readme.md

@@ -377,6 +377,11 @@ The class `Polyfill` includes the following extension methods:
  * `Boolean TryGetValue<T>(T, T&)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.hashset-1.trygetvalue)
 
 
+#### IDictionary<TKey,TValue>
+
+ * `Collections.ObjectModel.ReadOnlyDictionary<TKey,TValue> AsReadOnly<TKey, TValue>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-2(system-collections-generic-idictionary((-0-1))))
+
+
 #### IEnumerable<TSource>
 
  * `IEnumerable<KeyValuePair<TKey,TAccumulate>> AggregateBy<TSource, TKey, TAccumulate>(Func<TSource,TKey>, TAccumulate, Func<TAccumulate,TSource,TAccumulate>, IEqualityComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.aggregateby#system-linq-enumerable-aggregateby-3(system-collections-generic-ienumerable((-0))-system-func((-0-1))-system-func((-1-2))-system-func((-2-0-2))-system-collections-generic-iequalitycomparer((-1))))
@@ -392,6 +397,11 @@ The class `Polyfill` includes the following extension methods:
  * `HashSet<TSource> ToHashSet<TSource>(IEqualityComparer<TSource>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.tohashset#system-linq-enumerable-tohashset-1(system-collections-generic-ienumerable((-0))-system-collections-generic-iequalitycomparer((-0))))
 
 
+#### IList<T>
+
+ * `Collections.ObjectModel.ReadOnlyCollection<T> AsReadOnly<T>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-1(system-collections-generic-ilist((-0))))
+
+
 #### IReadOnlyDictionary<TKey,TValue>
 
  * `TValue GetValueOrDefault<TKey, TValue>(TKey)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.getvalueordefault)

src/Consume/Consume.cs

@@ -75,6 +75,12 @@ class Consume
         var startsWith = "value".StartsWith('a');
         var endsWith = "value".EndsWith('a');
 
+        IList<string> ilist = new List<string>();
+        ilist.AsReadOnly();
+
+        IDictionary<int, int> idictionary = new Dictionary<int, int>();
+        idictionary.AsReadOnly();
+
         var enumerable = (IEnumerable<string>) new List<string>
         {
             "a",

src/Polyfill/Polyfill_Dictionary.cs

@@ -2,15 +2,28 @@
 
 #pragma warning disable
 
-#if NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2X
-
 using System;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using System.Diagnostics.CodeAnalysis;
 using Link = System.ComponentModel.DescriptionAttribute;
 
 static partial class Polyfill
 {
+#if !NET7_0_OR_GREATER
+    /// <summary>
+    /// Returns a read-only <see cref="ReadOnlyDictionary{TKey,TValue}"/> wrapper for the current dictionary.
+    /// </summary>
+    /// <typeparam name="TKey">The type of keys in the dictionary.</typeparam>
+    /// <typeparam name="TValue">The type of values in the dictionary.</typeparam>
+    /// <param name="dictionary">The dictionary to wrap.</param>
+    /// <returns>An object that acts as a read-only wrapper around the current <see cref="IDictionary{TKey, TValue}"/>.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="dictionary"/> is null.</exception>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-2(system-collections-generic-idictionary((-0-1)))")]
+    public static ReadOnlyDictionary<TKey, TValue> AsReadOnly<TKey, TValue>(this IDictionary<TKey, TValue> target) =>
+        new(target);
+#endif
+#if NETFRAMEWORK || NETSTANDARD2_0 || NETCOREAPP2X
     /// <summary>
     /// Removes the value with the specified key from the <see cref="Dictionary{TKey,TValue}"/>, and copies the element
     /// to the value parameter.
@@ -24,12 +37,12 @@ static partial class Polyfill
     /// <exception cref="ArgumentNullException"><paramref name="key"/> is <code>null</code>.</exception>
     [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.dictionary-2.remove")]
     public static bool Remove<TKey, TValue>(
-        this Dictionary<TKey,TValue> target,
+        this Dictionary<TKey, TValue> target,
         TKey key,
         [MaybeNullWhen(false)] out TValue value)
     {
         target.TryGetValue(key, out value);
         return target.Remove(key);
     }
-}
-#endif
+#endif
+}

src/Polyfill/Polyfill_List.cs

@@ -2,25 +2,35 @@
 
 #pragma warning disable
 
-#if !NET8_0_OR_GREATER && FeatureMemory
 
 using System;
 using System.Collections.Generic;
+using System.Collections.ObjectModel;
 using Link = System.ComponentModel.DescriptionAttribute;
 
 static partial class Polyfill
 {
+#if !NET7_0_OR_GREATER
+
+    /// <summary>Returns a read-only <see cref="ReadOnlyCollection{T}" /> wrapper for the current collection.</summary>
+    /// <returns>An object that acts as a read-only wrapper around the current <see cref="IList{T}" />.</returns>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.asreadonly#system-collections-generic-collectionextensions-asreadonly-1(system-collections-generic-ilist((-0)))")]
+    public static ReadOnlyCollection<T> AsReadOnly<T>(this IList<T> target) =>
+        new(target);
+#endif
+
+#if !NET8_0_OR_GREATER && FeatureMemory
     /// <summary>Adds the elements of the specified span to the end of the <see cref="List{T}"/>.</summary>
     /// <typeparam name="T">The type of elements in the list.</typeparam>
     /// <param name="list">The list to which the elements should be added.</param>
     /// <param name="source">The span whose elements should be added to the end of the <see cref="List{T}"/>.</param>
     /// <exception cref="ArgumentNullException">The <paramref name="list"/> is null.</exception>
     [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.addrange")]
-    public static void AddRange<T>(this List<T> list, ReadOnlySpan<T> source)
+    public static void AddRange<T>(this List<T> target, ReadOnlySpan<T> source)
     {
         foreach (var item in source)
         {
-            list.Add(item);
+            target.Add(item);
         }
     }
 
@@ -32,12 +42,12 @@ public static void AddRange<T>(this List<T> list, ReadOnlySpan<T> source)
     /// <exception cref="ArgumentNullException">The <paramref name="list"/> is null.</exception>
     /// <exception cref="ArgumentOutOfRangeException"><paramref name="index"/> is less than 0 or greater than <paramref name="list"/>'s <see cref="List{T}.Count"/>.</exception>
     [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.insertrange")]
-    public static void InsertRange<T>(this List<T> list, int index, ReadOnlySpan<T> source)
+    public static void InsertRange<T>(this List<T> target, int index, ReadOnlySpan<T> source)
     {
         for (var i = 0; i < source.Length; i++)
         {
             var item = source[i];
-            list.Insert(i + index, item);
+            target.Insert(i + index, item);
         }
     }
 
@@ -48,12 +58,12 @@ public static void InsertRange<T>(this List<T> list, int index, ReadOnlySpan<T>
     /// <exception cref="ArgumentNullException">The <paramref name="list"/> is null.</exception>
     /// <exception cref="ArgumentException">The number of elements in the source <see cref="List{T}"/> is greater than the number of elements that the destination span can contain.</exception>
     [Link("https://learn.microsoft.com/en-us/dotnet/api/system.collections.generic.collectionextensions.copyto?view=net-8.0")]
-    public static void CopyTo<T>(this List<T> list, Span<T> destination)
+    public static void CopyTo<T>(this List<T> target, Span<T> destination)
     {
-        for (var index = 0; index < list.Count; index++)
+        for (var index = 0; index < target.Count; index++)
         {
-            destination[index] = list[index];
+            destination[index] = target[index];
         }
     }
-}
-#endif
+#endif
+}

src/Tests/PolyfillTests_Dictionary.cs

@@ -1,5 +1,17 @@
 partial class PolyfillTests
 {
+    [Test]
+    public void IReadOnlyDictionaryAsReadOnly()
+    {
+        IDictionary<string, string> dictionary = new Dictionary<string,string>
+        {
+            {"key", "value"}
+        };
+
+        var readOnly = dictionary.AsReadOnly();
+        Assert.AreEqual("value", readOnly["key"]);
+    }
+
     [Test]
     public void Dictionary_Remove()
     {

src/Tests/PolyfillTests_List.cs

@@ -1,5 +1,16 @@
 partial class PolyfillTests
 {
+    [Test]
+    public void IListAsReadOnly()
+    {
+        IList<char> list = new List<char>
+        {
+            'a'
+        };
+        var readOnly = list.AsReadOnly();
+        Assert.AreEqual('a', readOnly[0]);
+    }
+
     [Test]
     public void ListAddRangeReadOnlySpan()
     {