What's New - .NET 10 Preview 1

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docs/core/whats-new/dotnet-10/libraries.md

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+---
+title: What's new in .NET libraries for .NET 10
+description: Learn about the new .NET libraries features introduced in .NET 10.
+titleSuffix: ""
+ms.date: 02/20/2025
+ms.topic: whats-new
+ai-usage: ai-assisted
+---
+
+# What's new in .NET libraries for .NET 10
+
+This article describes new features in the .NET libraries for .NET 10. It has been updated for Preview 1.
+
+## Find certificates by thumbprints other than SHA-1
+
+Finding certificates uniquely by thumbprint is a fairly common operation, but the <xref:System.Security.Cryptography.X509Certificates.X509Certificate2Collection.Find(System.Security.Cryptography.X509Certificates.X509FindType,System.Object,System.Boolean)?displayProperty=nameWithType> method (for the <xref:System.Security.Cryptography.X509Certificates.X509FindType.FindByThumbprint> mode) only searches for the SHA-1 Thumbprint value.
+
+Since SHA-2-256 ("SHA256") and SHA-3-256 have the same lengths, it doesn't make sense to implement the `Find` method to find any *vaguely* matching thumbprints.
+
+Instead, .NET 10 introduces a new method that accepts the name of the hash algorithm to use for matching.
+
+```csharp
+X509Certificate2Collection coll = store.Certificates.FindByThumbprint(HashAlgorithmName.SHA256, thumbprint);
+Debug.Assert(coll.Count < 2, "Collection has too many matches, has SHA-2 been broken?");
+return coll.SingleOrDefault();
+```
+
+## Find PEM-encoded Data in ASCII/UTF-8
+
+The PEM encoding (originally "Privacy Enhanced Mail", but now used widely outside of email) is defined for "text", which means that the <xref:System.Security.Cryptography.PemEncoding> class was designed to run on <xref:System.String> and `ReadOnlySpan<char>`. However, it's quite common (especially on Linux) to have something like a certificate written in a file that uses the ASCII (string) encoding. Historically, that meant you needed to open the file and convert the bytes to chars (or a string) before you could use `PemEncoding`.
+
+Taking advantage of the fact that PEM is only defined for 7-bit ASCII characters, and that 7-bit ASCII has a perfect overlap with single-byte UTF-8 values, you can now skip the UTF-8/ASCII-to-char conversion and read the file directly.
+
+```diff
+byte[] fileContents = File.ReadAllBytes(path);
+-char[] text = Encoding.ASCII.GetString(fileContents);
+-PemFields pemFields = PemEncoding.Find(text);
++PemFields pemFields = PemEncoding.FindUtf8(fileContents);
+
+-byte[] contents = Base64.DecodeFromChars(text.AsSpan()[pemFields.Base64Data]);
++byte[] contents = Base64.DecodeFromUtf8(fileContents.AsSpan()[pemFields.Base64Data]);
+```
+
+## New method overloads in ISOWeek for DateOnly type
+
+The <xref:System.Globalization.ISOWeek> class was originally designed to work exclusively with <xref:System.DateTime>, as it was introduced before the <xref:System.DateOnly> type existed. Now that `DateOnly` is available, it makes sense for `ISOWeek` to support it as well.
+
+```csharp
+public static class ISOWeek
+{
+    // New overloads
+    public static int GetWeekOfYear(DateOnly date);
+    public static int GetYear(DateOnly date);
+    public static DateOnly ToDateOnly(int year, int week, DayOfWeek dayOfWeek);
+}
+```
+
+## String normalization APIs to work with span of characters
+
+Unicode string normalization has been supported for a long time, but existing APIs have only worked with the string type. This means that callers with data stored in different forms, such as character arrays or spans, must allocate a new string to use these APIs. Additionally, APIs that return a normalized string always allocate a new string to represent the normalized output.
+
+.NET 10 introduces new APIs that work with spans of characters, expanding normalization beyond string types and helping to avoid unnecessary allocations.
+
+```csharp
+public static class StringNormalizationExtensions
+{
+    public static int GetNormalizedLength(this ReadOnlySpan<char> source, NormalizationForm normalizationForm = NormalizationForm.FormC);
+    public static bool IsNormalized(this ReadOnlySpan<char> source, NormalizationForm normalizationForm = NormalizationForm.FormC);
+    public static bool TryNormalize(this ReadOnlySpan<char> source, Span<char> destination, out int charsWritten, NormalizationForm normalizationForm = NormalizationForm.FormC);
+}
+```
+
+## Numeric ordering for string comparison
+
+Numerical string comparison is a highly requested feature for comparing strings numerically instead of lexicographically. For example, `2` is less than `10`, so `"2"` should appear before `"10"` when ordered numerically. Similarly, `"2"` and `"02"` are equal numerically. With the new `CompareOptions.NumericOrdering` <!--xref:System.Globalization.CompareOptions.NumericOrdering--> option, it's now possible to do these types of comparisons:
+
+:::code language="csharp" source="../snippets/dotnet-10/csharp/snippets.cs" id="snippet3":::
+
+Note that this option is not valid for the following index-based string operations: `IndexOf`, `LastIndexOf`, `StartsWith`, `EndsWith`, `IsPrefix`, and `IsSuffix`.
+
+## New `TimeSpan.FromMilliseconds` overload with single parameter
+
+The <xref:System.TimeSpan.FromMilliseconds(System.Int64,System.Int64)?displayProperty=nameWithType> method was introduced previously without adding an overload that takes a single parameter.
+
+Although this works since the second parameter is optional, it causes a compilation error when used in a LINQ expression like:
+
+```csharp
+Expression<Action> a = () => TimeSpan.FromMilliseconds(1000);
+```
+
+The issue arises because LINQ expressions cannot handle optional parameters. To address this, .NET 10 introduces an overload takes a single parameter and modifying the existing method to make the second parameter mandatory:
+
+```csharp
+public readonly struct TimeSpan
+{
+    public static TimeSpan FromMilliseconds(long milliseconds, long microseconds); // Second parameter is no longer optional
+    public static TimeSpan FromMilliseconds(long milliseconds);  // New overload
+}
+```
+
+## ZipArchive performance and memory improvements
+
+.NET 10 improves the performance and memory usage of <xref:System.IO.Compression.ZipArchive>.
+
+First, the way entries are written to a `ZipArchive` when in `Update` mode has been optimized. Previously, all <xref:System.IO.Compression.ZipArchiveEntry> instances were loaded into memory and rewritten, which could lead to high memory usage and performance bottlenecks. The optimization reduces memory usage and improves performance by avoiding the need to load all entries into memory. Details are provided in [dotnet/runtime #102704](https://github.com/dotnet/runtime/pull/102704#issue-2317941700).
+
+Second, the extraction of <xref:System.IO.Compression.ZipArchive> entries is now parallelized, and internal data structures are optimized for better memory usage. These improvements address issues related to performance bottlenecks and high memory usage, making `ZipArchive` more efficient and faster, especially when dealing with large archives. Details are provided [dotnet/runtime #103153](https://github.com/dotnet/runtime/pull/103153#issue-2339713028).
+
+## Additional `TryAdd` and `TryGetValue` overloads for `OrderedDictionary<TKey, TValue>`
+
+<xref:System.Collections.Generic.OrderedDictionary`2> provides `TryAdd` and `TryGetValue` for addition and retrieval like any other `IDictionary<TKey, TValue>` implementation. However, there are scenarios where you might want to perform additional operations, so new overloads have been added that return an index to the entry:
+
+```csharp
+public class OrderedDictionary<TKey, TValue>
+{
+    // New overloads
+    public bool TryAdd(TKey key, TValue value, out int index);
+    public bool TryGetValue(TKey key, out TValue value, out int index);
+}
+```
+
+This index can then be used with <xref:System.Collections.Generic.OrderedDictionary`2.GetAt*>/<xref:System.Collections.Generic.OrderedDictionary`2.SetAt*> for fast access to the entry. An example usage of the new `TryAdd` overload is to add or update a key/value pair in the ordered dictionary:
+
+:::code language="csharp" source="../snippets/dotnet-10/csharp/snippets.cs" id="snippet2":::
+
+This new API is already used in <xref:System.Json.JsonObject> and improves the performance of updating properties by 10-20%.
+
+## Allow specifying ReferenceHandler in `JsonSourceGenerationOptions`
+
+When using source generators for JSON serialization, the generated context will throw when cycles are serialized or deserialized. This behavior can now be customized by specifying the <xref:System.Text.Json.Serialization.ReferenceHandler> in the <xref:System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute>. Here is an example using `JsonKnownReferenceHandler.Preserve`:
+
+:::code language="csharp" source="../snippets/dotnet-10/csharp/snippets.cs" id="snippet3":::
+
+## More left-handed matrix transformation methods
+
+.NET 10 adds the remaining APIs for creating left-handed transformation matrices for billboard and constrained-billboard matrices. You can use these methods like their existing right-handed counterparts [add xrefs to the existing counterparts] when using a left-handed coordinate system instead.
+
+```csharp
+public partial struct Matrix4x4
+{
+   public static Matrix4x4 CreateBillboardLeftHanded(Vector3 objectPosition, Vector3 cameraPosition, Vector3 cameraUpVector, Vector3 cameraForwardVector)
+## More left-handed matrix transformation methods
+}
+```

docs/core/whats-new/dotnet-10/overview.md

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+---
+title: What's new in .NET 10
+description: Learn about the new features introduced in .NET 10 for the runtime, libraries, and SDK. Also find links to what's new in other areas, such as ASP.NET Core.
+titleSuffix: ""
+ms.date: 02/20/2025
+ms.topic: whats-new
+ai-usage: ai-assisted
+---
+
+# What's new in .NET 10
+
+Learn about the new features in .NET 10 and find links to further documentation. This page has been updated for Preview 1.
+
+## .NET runtime
+
+.NET 10, the successor to [.NET 9](../dotnet-9/overview.md), has a special focus on cloud-native apps and performance. It will be [supported for 3 years](https://dotnet.microsoft.com/platform/support/policy/dotnet-core) as a long-term support (LTS) release. You can [download .NET 10 here](https://get.dot.net/10).
+
+Your feedback is important and appreciated. We've created a discussion on [GitHub](https://github.com/dotnet/core/discussions/categories/news) for your questions and comments.
+
+For more information, see [What's new in the .NET 10 runtime](runtime.md).
+
+## .NET libraries
+
+The .NET 10 libraries introduce several new features and improvements. A new method `FindByThumbprint` allows finding certificates by thumbprints using hash algorithms other than SHA-1. Additionally, support has been added for reading PEM-encoded data directly from ASCII encoded files. The <xref:System.Globalization.ISOWeek> class now includes new method overloads to support the <xref:System.DateOnly> type. Unicode string normalization APIs have been enhanced to work with spans of characters, and a new `CompareOptions.NumericOrdering` option has been introduced for numerical string comparison.
+
+Additionally, a new <xref:System.TimeSpan.FromMilliseconds*?displayProperty=nameWithType> overload that takes a single parameter has been added. The performance and memory usage of [ZipArchive](xref:System.IO.Compression.ZipArchive) have been improved. New `TryAdd` and `TryGetValue` overloads for <xref:System.Collections.Generic.OrderedDictionary`2?displayProperty=nameWithType> now return an index to the entry. JSON serialization has been enhanced by allowing the specification of <xref:System.Text.Json.Serialization.ReferenceHandler> in <xref:System.Text.Json.Serialization.JsonSourceGenerationOptionsAttribute>. Lastly, new APIs have been introduced for creating left-handed transformation matrices for billboard and constrained-billboard matrices.
+
+For more information, see [What's new in the .NET 10 libraries](libraries.md).
+
+## .NET SDK
+
+The .NET 10 SDK introduces following new features and enhancements:
+
+- [Pruning of Framework-provided Package References](sdk.md#pruning-of-framework-provided-package-references)
+
+For more information, see [What's new in the SDK for .NET 10](sdk.md).
+
+## .NET Aspire
+
+.NET Aspire releases version 9.1, which focuses on quality of life fixes.
+
+For more information, see [.NET Aspire — what's new?](/dotnet/aspire/whats-new/).
+
+## ASP.NET Core
+
+Changes in ASP.NET Core 10.0 include:
+
+- Blazor: Added new features for Blazor, including the QuickGrid RowClass parameter and Blazor script serving as a static web asset.
+- SignalR: Added new features for SignalR.
+- Minimal APIs: Added new features for minimal APIs.
+- OpenAPI: Added support for generating OpenAPI version 3.1 documents and serving the generated OpenAPI document in YAML format.
+- Authentication and authorization: Added new features for authentication and authorization.
+- Miscellaneous: Added better support for testing apps with top-level statements and a new helper method for detecting local URLs.
+
+For more information, see [What's new in ASP.NET Core for .NET 10](/aspnet/core/release-notes/aspnetcore-10.0).
+
+## .NET MAUI
+
+<!-- TODO - Add a brief overview of the new features in .NET MAUI for .NET 10. -->
+
+## EF Core
+
+Changes for EF Core 10 include:
+
+- LINQ and SQL translation enhancements.
+- ExecuteUpdateAsync now accepts a regular, non-expression lambda.
+
+For more information, see [What's new in EF Core for .NET 10](/ef/core/what-is-new/ef-core-10.0/whatsnew).
+
+## C# 14
+
+C# 14 introduces several new features and enhancements to improve developer productivity and code quality. Some of the key updates include:
+
+- `nameof` in unbound generics.
+- Implicit span conversions.
+- `field` backed properties.
+- Modifiers on simple lambda parameters.
+- Experimental feature - String literals in data section.
+
+For more information, see [What's new in C# 14](https://github.com/dotnet/core/blob/dotnet10p1/release-notes/10.0/preview/preview1/csharp.md).
+
+## Windows Forms
+
+Changes in Windows Forms for .NET 10 include:
+
+- Clipboard related serialization and deserialization changes.
+- Obsoleted Clipboard APIs.
+- New Clipboard related APIs.
+
+For more information, see [What's new in Windows Forms for .NET 10](https://github.com/dotnet/core/blob/dotnet10p1/release-notes/10.0/preview/preview1/winforms.md).
+
+## See also
+
+- [.NET 10 Preview 1 container image updates](https://github.com/dotnet/core/blob/dotnet10p1/release-notes/10.0/preview/preview1/containers.md)
+- [F# updates in .NET 10 Preview 1](https://github.com/dotnet/core/blob/dotnet10p1/release-notes/10.0/preview/preview1/fsharp.md)
+- [Visual Basic updates in .NET 10 Preview 1](https://github.com/dotnet/core/blob/dotnet10p1/release-notes/10.0/preview/preview1/visualbasic.md)

docs/core/whats-new/dotnet-10/runtime.md

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+---
+title: What's new in .NET 10 runtime
+description: Learn about the new .NET features introduced in the .NET 10 runtime.
+titleSuffix: ""
+ms.date: 02/20/2025
+ms.topic: whats-new
+ai-usage: ai-assisted
+---
+# What's new in the .NET 10 runtime
+
+This article describes new features and performance improvements in the .NET runtime for .NET 10. It has been updated for Preview 1.
+
+## Array interface method devirtualization
+
+One of the code generation team's [focus areas](https://github.com/dotnet/runtime/issues/108988) for .NET 10 is to reduce the abstraction overhead of popular language features. In pursuit of this goal, the JIT's ability to devirtualize method calls has been expanded to cover array interface methods.
+
+Consider the typical approach of looping over an array:
+
+```csharp
+static int Sum(int[] array)
+{
+    int sum = 0;
+    for (int i = 0; i < array.Length; i++)
+    {
+        sum += array[i];
+    }
+    return sum;
+}
+```
+
+This code shape is easy for the JIT to optimize, mainly because there aren't any virtual calls to reason about. Instead, the JIT can focus on removing bounds checks on the array access and applying the [loop optimizations that were added in .NET 9](https://devblogs.microsoft.com/dotnet/performance-improvements-in-net-9/). The following example adds some virtual calls:
+
+```csharp
+static int Sum(int[] array)
+{
+    int sum = 0;
+    IEnumerable<int> temp = array;
+
+    foreach (var num in temp)
+    {
+        sum += num;
+    }
+    return sum;
+}
+```
+
+The type of the underlying collection is clear, and the JIT should be able to transform this snippet into the first one. However, array interfaces are implemented differently from "normal" interfaces, such that the JIT does not know how to devirtualize them. This means the enumerator calls in the `for-each` loop remain virtual, blocking multiple optimizations such as inlining and stack allocation.
+
+Starting in .NET 10, the JIT can devirtualize and inline array interface methods. This is the first of many steps to achieve performance parity between the implementations, as detailed in the [.NET 10 de-abstraction plans](https://github.com/dotnet/runtime/issues/108913).
+
+## Stack allocation of arrays of value types
+
+In .NET 9, the JIT gained the ability to allocate objects on the stack, when the object is guaranteed to not outlive its parent method. Not only does stack allocation reduce the number of objects the GC has to track, but it also unlocks other optimizations. For example, after an object has been stack-allocated, the JIT can consider replacing it entirely with its scalar values. Because of this, stack allocation is key to reducing the abstraction penalty of reference types.
+
+In .NET 10, the JIT now stack-allocates small, fixed-sized arrays of value types that don't contain GC pointers when it can make the same lifetime guarantees described previously. Consider the following example:
+
+```csharp
+static void Sum()
+{
+    int[] numbers = {1, 2, 3};
+    int sum = 0;
+
+    for (int i = 0; i < numbers.Length; i++)
+    {
+        sum += numbers[i];
+    }
+
+    Console.WriteLine(sum);
+}
+
+```
+
+Because the JIT knows `numbers` is an array of only three integers at compile time, and it doesn't outlive a call to `Sum`, it allocates it on the stack.
+
+## AVX10.2 support
+
+.NET 10 introduces support for the Advanced Vector Extensions (AVX) 10.2 for x64-based processors. The new intrinsics available in the `System.Runtime.Intrinsics.X86.Avx10v2` <!--xref:System.Runtime.Intrinsics.X86.Avx10v2--> class can be tested once capable hardware is available.
+
+Because AVX10.2-enabled hardware is not yet available, the JIT's support for AVX10.2 is currently disabled by default.