IEnumerable in C#: retarget net10.0, Book record, GenericLibrary with yield return, LibraryTests (#2297)

Both projects net7.0 to net10.0. Microsoft.NET.Test.Sdk 18.11.0, xunit 2.9.3, xunit.runner.visualstudio 4.0.1, coverlet.collector 10.1.0. Book becomes a positional record, the Library constructor copies with a collection expression, Program.cs moves to top-level statements and gains the GenericLibrary query, file-scoped namespaces. New GenericLibrary implements IEnumerable<Book> with yield return. The test project references the console project and gains LibraryTests (iteration order from the -1 start, Cast before LINQ on the non-generic Library, LINQ directly on GenericLibrary, Reset on the generated enumerator throws NotSupportedException).

Author: vladimir-pecanac-main

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/Book.cs

@@ -1,14 +1,3 @@
-namespace IEnumerableCSharp
-{
-    public class Book
-    {
-        public Book(string name, string author)
-        {
-            Name = name;
-            Author = author;
-        }
+namespace IEnumerableCSharp;
 
-        public string Name { get; set; }
-        public string Author { get; set; }
-    }
-}
+public record Book(string Name, string Author);

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/BookEnumerator.cs

@@ -1,36 +1,35 @@
 using System.Collections;
 
-namespace IEnumerableCSharp
+namespace IEnumerableCSharp;
+
+public class BookEnumerator : IEnumerator
 {
-    public class BookEnumerator : IEnumerator
-    {
-        private readonly Book[] _books;
-        private int _index = -1;
+    private readonly Book[] _books;
+    private int _index = -1;
 
-        public BookEnumerator(Book[] books)
-        {
-            _books = books;
-        }
+    public BookEnumerator(Book[] books)
+    {
+        _books = books;
+    }
 
-        public Book Current
+    public Book Current
+    {
+        get
         {
-            get
-            {
-                return _books[_index];
-            }
+            return _books[_index];
         }
+    }
 
-        object IEnumerator.Current => Current;
+    object IEnumerator.Current => Current;
 
-        public bool MoveNext()
-        {
-            _index++;
-            return _index < _books.Length;
-        }
+    public bool MoveNext()
+    {
+        _index++;
+        return _index < _books.Length;
+    }
 
-        public void Reset()
-        {
-            _index = -1;
-        }
+    public void Reset()
+    {
+        _index = -1;
     }
 }

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/GenericLibrary.cs

@@ -0,0 +1,23 @@
+using System.Collections;
+
+namespace IEnumerableCSharp;
+
+public class GenericLibrary : IEnumerable<Book>
+{
+    private readonly Book[] _books;
+
+    public GenericLibrary(Book[] books)
+    {
+        _books = [.. books];
+    }
+
+    public IEnumerator<Book> GetEnumerator()
+    {
+        foreach (var book in _books)
+        {
+            yield return book;
+        }
+    }
+
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
+}

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/IEnumerableCSharp.csproj

@@ -2,7 +2,7 @@
 
   <PropertyGroup>
     <OutputType>Exe</OutputType>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
   </PropertyGroup>

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/Library.cs

@@ -1,24 +1,17 @@
 using System.Collections;
 
-namespace IEnumerableCSharp
+namespace IEnumerableCSharp;
+
+public class Library : IEnumerable
 {
-    public class Library : IEnumerable
-    {
-        private readonly Book[] _books;
+    private readonly Book[] _books;
 
-        public Library(Book[] books)
-        {
-            _books = new Book[books.Length];
+    public Library(Book[] books)
+    {
+        _books = [.. books];
+    }
 
-            for (int i = 0; i < books.Length; i++)
-            {
-                _books[i] = books[i];
-            }
-        }
+    public BookEnumerator GetEnumerator() => new BookEnumerator(_books);
 
-        public BookEnumerator GetEnumerator() => new BookEnumerator(_books);
-        
-        IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
-        
-    }
+    IEnumerator IEnumerable.GetEnumerator() => GetEnumerator();
 }

collections-csharp/IEnumerableCSharp/IEnumerableCSharp/Program.cs

@@ -1,24 +1,26 @@
-namespace IEnumerableCSharp
+using IEnumerableCSharp;
+
+Book[] books =
+[
+    new("Anna Karenina", "Leo Tolstoy"),
+    new("To Kill a Mockingbird", "Harper Lee"),
+    new("The Great Gatsby", "F. Scott Fitzgerald"),
+    new("One Hundred Years of Solitude", "Gabriel García Márquez"),
+    new("A Passage to India", "E.M. Forster")
+];
+
+var library = new Library(books);
+
+foreach (var book in library)
 {
-    internal class Program
-    {
-        static void Main(string[] args)
-        {
-            var books = new Book[5]
-            {
-                new Book("Anna Karenina", "Leo Tolstoy"),
-                new Book("To Kill a Mockingbird", "Harper Lee"),
-                new Book("The Great Gatsby", "F. Scott Fitzgerald"),
-                new Book("One Hundred Years of Solitude", "Gabriel García Márquez"),
-                new Book("A Passage to India", "E.M. Forster")
-            };
+    Console.WriteLine($"Book: {book.Name}, Author: {book.Author}");
+}
 
-            var library = new Library(books);
+var genericLibrary = new GenericLibrary(books);
 
-            foreach (var book in library)
-            {
-                Console.WriteLine($"Book: {book.Name}, Author: {book.Author}");
-            }
-        }
-    }
-}
+var tolstoy = genericLibrary.Where(book => book.Author == "Leo Tolstoy");
+
+foreach (var book in tolstoy)
+{
+    Console.WriteLine($"By Tolstoy: {book.Name}");
+}

collections-csharp/IEnumerableCSharp/Tests/LibraryTests.cs

@@ -0,0 +1,51 @@
+using System.Collections;
+using IEnumerableCSharp;
+
+namespace Tests;
+
+public class LibraryTests
+{
+    private static readonly Book[] Books =
+    [
+        new("Anna Karenina", "Leo Tolstoy"),
+        new("To Kill a Mockingbird", "Harper Lee"),
+        new("War and Peace", "Leo Tolstoy")
+    ];
+
+    [Fact]
+    public void WhenIteratingLibrary_ThenEveryBookComesBackInOrder()
+    {
+        var names = new List<string>();
+
+        foreach (var book in new Library(Books))
+        {
+            names.Add(book.Name);
+        }
+
+        Assert.Equal(["Anna Karenina", "To Kill a Mockingbird", "War and Peace"], names);
+    }
+
+    [Fact]
+    public void WhenUsingLinqOnNonGenericLibrary_ThenCastIsNeeded()
+    {
+        var tolstoy = new Library(Books).Cast<Book>().Where(book => book.Author == "Leo Tolstoy");
+
+        Assert.Equal(2, tolstoy.Count());
+    }
+
+    [Fact]
+    public void WhenUsingLinqOnGenericLibrary_ThenNoCastIsNeeded()
+    {
+        var tolstoy = new GenericLibrary(Books).Where(book => book.Author == "Leo Tolstoy");
+
+        Assert.Equal(2, tolstoy.Count());
+    }
+
+    [Fact]
+    public void WhenResettingIteratorEnumerator_ThenNotSupportedExceptionIsThrown()
+    {
+        using var enumerator = new GenericLibrary(Books).GetEnumerator();
+
+        Assert.Throws<NotSupportedException>(() => enumerator.Reset());
+    }
+}

collections-csharp/IEnumerableCSharp/Tests/Tests.csproj

@@ -1,24 +1,28 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>net7.0</TargetFramework>
+    <TargetFramework>net10.0</TargetFramework>
     <ImplicitUsings>enable</ImplicitUsings>
     <Nullable>enable</Nullable>
 
     <IsPackable>false</IsPackable>
   </PropertyGroup>
 
   <ItemGroup>
-    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="17.1.0" />
-    <PackageReference Include="xunit" Version="2.4.1" />
-    <PackageReference Include="xunit.runner.visualstudio" Version="2.4.3">
+    <PackageReference Include="Microsoft.NET.Test.Sdk" Version="18.11.0" />
+    <PackageReference Include="xunit" Version="2.9.3" />
+    <PackageReference Include="xunit.runner.visualstudio" Version="4.0.1">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
-    <PackageReference Include="coverlet.collector" Version="3.1.2">
+    <PackageReference Include="coverlet.collector" Version="10.1.0">
       <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
       <PrivateAssets>all</PrivateAssets>
     </PackageReference>
   </ItemGroup>
 
+  <ItemGroup>
+    <ProjectReference Include="../IEnumerableCSharp/IEnumerableCSharp.csproj" />
+  </ItemGroup>
+
 </Project>