add FirstOrDefault with override default

apiCount.include.md

@@ -1 +1 @@
-**API count: 215**
+**API count: 217**

api_list.include.md

@@ -53,6 +53,8 @@
  * `IEnumerable<TSource> Except<TSource>(IEqualityComparer<TSource>, TSource[])` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.except#system-linq-enumerable-except-1(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-0))-system-collections-generic-iequalitycomparer((-0))))
  * `IEnumerable<TSource> ExceptBy<TSource, TKey>(IEnumerable<TKey>, Func<TSource,TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.exceptby#system-linq-enumerable-exceptby-2(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-1))-system-func((-0-1))))
  * `IEnumerable<TSource> ExceptBy<TSource, TKey>(IEnumerable<TKey>, Func<TSource,TKey>, IEqualityComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.exceptby#system-linq-enumerable-exceptby-2(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-1))-system-func((-0-1))-system-collections-generic-iequalitycomparer((-1))))
+ * `TSource FirstOrDefault<TSource>(Func<TSource,Boolean>, TSource)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-system-func((-0-system-boolean))-0))
+ * `TSource FirstOrDefault<TSource>(TSource)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-0))
  * `IEnumerable<ValueTuple<Int32,TSource>> Index<TSource>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.index#system-linq-enumerable-index-1(system-collections-generic-ienumerable((-0))))
  * `TSource MaxBy<TSource, TKey>(Func<TSource,TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.maxby#system-linq-enumerable-maxby-2(system-collections-generic-ienumerable((-0))-system-func((-0-1))))
  * `TSource MaxBy<TSource, TKey>(Func<TSource,TKey>, IComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.maxby?view=net-8.0#system-linq-enumerable-maxby-2(system-collections-generic-ienumerable((-0))-system-func((-0-1))-system-collections-generic-icomparer((-1))))

notes.txt

@@ -5,8 +5,6 @@ https://github.com/dotnet/core/blob/main/release-notes/8.0/8.0.0/api-diff/Micros
 https://github.com/dotnet/core/blob/main/release-notes/7.0/7.0.0/api-diff/Microsoft.NETCore.App/7.0.0_System.Collections.Immutable.md
 
 
-public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, TSource defaultValue);
-public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, TSource defaultValue);
 public static IEnumerable<TSource> IntersectBy<TSource, TKey>(this IEnumerable<TSource> first, IEnumerable<TKey> second, Func<TSource, TKey> keySelector);
 public static IEnumerable<TSource> IntersectBy<TSource, TKey>(this IEnumerable<TSource> first, IEnumerable<TKey> second, Func<TSource, TKey> keySelector, IEqualityComparer<TKey> comparer);
 public static TSource LastOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, TSource defaultValue);

readme.md

@@ -12,7 +12,7 @@ The package targets `netstandard2.0` and is designed to support the following ru
  * `net5.0`, `net6.0`, `net7.0`, `net8.0`, `net9.0`
 
 
-**API count: 215**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
+**API count: 217**<!-- singleLineInclude: apiCount. path: /apiCount.include.md -->
 
 
 **See [Milestones](../../milestones?state=closed) for release notes.**
@@ -413,6 +413,8 @@ The class `Polyfill` includes the following extension methods:
  * `IEnumerable<TSource> Except<TSource>(IEqualityComparer<TSource>, TSource[])` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.except#system-linq-enumerable-except-1(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-0))-system-collections-generic-iequalitycomparer((-0))))
  * `IEnumerable<TSource> ExceptBy<TSource, TKey>(IEnumerable<TKey>, Func<TSource,TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.exceptby#system-linq-enumerable-exceptby-2(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-1))-system-func((-0-1))))
  * `IEnumerable<TSource> ExceptBy<TSource, TKey>(IEnumerable<TKey>, Func<TSource,TKey>, IEqualityComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.exceptby#system-linq-enumerable-exceptby-2(system-collections-generic-ienumerable((-0))-system-collections-generic-ienumerable((-1))-system-func((-0-1))-system-collections-generic-iequalitycomparer((-1))))
+ * `TSource FirstOrDefault<TSource>(Func<TSource,Boolean>, TSource)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-system-func((-0-system-boolean))-0))
+ * `TSource FirstOrDefault<TSource>(TSource)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-0))
  * `IEnumerable<ValueTuple<Int32,TSource>> Index<TSource>()` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.index#system-linq-enumerable-index-1(system-collections-generic-ienumerable((-0))))
  * `TSource MaxBy<TSource, TKey>(Func<TSource,TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.maxby#system-linq-enumerable-maxby-2(system-collections-generic-ienumerable((-0))-system-func((-0-1))))
  * `TSource MaxBy<TSource, TKey>(Func<TSource,TKey>, IComparer<TKey>)` [reference](https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.maxby?view=net-8.0#system-linq-enumerable-maxby-2(system-collections-generic-ienumerable((-0))-system-func((-0-1))-system-collections-generic-icomparer((-1))))

src/Polyfill/Polyfill_IEnumerable_FirstOrDefault.cs

@@ -0,0 +1,86 @@
+// <auto-generated />
+
+#pragma warning disable
+
+using System;
+using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
+using Link = System.ComponentModel.DescriptionAttribute;
+using System.Linq;
+
+static partial class Polyfill
+{
+#if !NET6_0_OR_GREATER
+
+    /// <summary>Returns the first element of the sequence that satisfies a condition or a default value if no such element is found.</summary>
+    /// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
+    /// <param name="source">An <see cref="IEnumerable{T}" /> to return an element from.</param>
+    /// <param name="predicate">A function to test each element for a condition.</param>
+    /// <param name="defaultValue">The default value to return if the sequence is empty.</param>
+    /// <returns><paramref name="defaultValue" /> if <paramref name="source" /> is empty or if no element passes the test specified by <paramref name="predicate" />; otherwise, the first element in <paramref name="source" /> that passes the test specified by <paramref name="predicate" />.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="source" /> or <paramref name="predicate" /> is <see langword="null" />.</exception>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-system-func((-0-system-boolean))-0)")]
+    public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, TSource defaultValue)
+    {
+        TSource? first = source.TryGetFirst(predicate, out bool found);
+        return found ? first! : defaultValue;
+    }
+
+    /// <summary>Returns the first element of a sequence, or a default value if the sequence contains no elements.</summary>
+    /// <typeparam name="TSource">The type of the elements of <paramref name="source" />.</typeparam>
+    /// <param name="source">The <see cref="IEnumerable{T}" /> to return the first element of.</param>
+    /// <param name="defaultValue">The default value to return if the sequence is empty.</param>
+    /// <returns><paramref name="defaultValue" /> if <paramref name="source" /> is empty; otherwise, the first element in <paramref name="source" />.</returns>
+    /// <exception cref="ArgumentNullException"><paramref name="source" /> is <see langword="null" />.</exception>
+    [Link("https://learn.microsoft.com/en-us/dotnet/api/system.linq.enumerable.firstordefault#system-linq-enumerable-firstordefault-1(system-collections-generic-ienumerable((-0))-0)")]
+    public static TSource FirstOrDefault<TSource>(this IEnumerable<TSource> source, TSource defaultValue)
+    {
+        TSource? first = source.TryGetFirst(out bool found);
+        return found ? first! : defaultValue;
+    }
+
+    static TSource? TryGetFirst<TSource>(this IEnumerable<TSource> source, out bool found) =>
+        TryGetFirstNonIterator(source, out found);
+
+    static TSource? TryGetFirstNonIterator<TSource>(IEnumerable<TSource> source, out bool found)
+    {
+        if (source is IList<TSource> list)
+        {
+            if (list.Count > 0)
+            {
+                found = true;
+                return list[0];
+            }
+        }
+        else
+        {
+            using (IEnumerator<TSource> e = source.GetEnumerator())
+            {
+                if (e.MoveNext())
+                {
+                    found = true;
+                    return e.Current;
+                }
+            }
+        }
+
+        found = false;
+        return default;
+    }
+
+    static TSource? TryGetFirst<TSource>(this IEnumerable<TSource> source, Func<TSource, bool> predicate, out bool found)
+    {
+        foreach (TSource element in source)
+        {
+            if (predicate(element))
+            {
+                found = true;
+                return element;
+            }
+        }
+
+        found = false;
+        return default;
+    }
+#endif
+}

src/Tests/PolyfillTests_IEnumerable.cs

@@ -191,6 +191,15 @@ public void ElementAtIndex()
     }
 #endif
 
+    [Test]
+    public void FirstOrDefault()
+    {
+        IEnumerable<int> list = new List<int> { 1, 2 };
+
+        Assert.AreEqual(2, list.FirstOrDefault(_ => _ == 2, 3));
+        Assert.AreEqual(3, Enumerable.Empty<int>().FirstOrDefault(3));
+    }
+
     [Test]
     public void Zip2()
     {