# Dotnet 10

> Provides up-to-date knowledge about .NET 10 and C# 14 for WPF application development. Use this skill when developing WPF apps targeting .NET 10, or when asked about .NET 10 / C# 14 features.

- Skill: `runceel/dotnet-10` (Agent Skill)
- Install (CLI): `npx skillmds@latest add runceel/dotnet-10`
- Raw SKILL.md: https://api.skillmd.com/api/skills/runceel/dotnet-10/raw
- Safety review: pending (external: skill-scanner PASS, skillspector PASS)
- Works with: Claude Code, Claude.ai, OpenAI Codex
- Category: Coding & Dev Tools
- Author: runceel (https://skillmd.com/u/runceel)
- Updated: 2026-09-10
- Page: https://skillmd.com/skills/runceel/dotnet-10

---


# .NET 10 + C# 14 WPF Development Reference

.NET 10 is an LTS release (released November 2025, supported for 3 years). The paired language version is C# 14. The required tooling is .NET 10 SDK and Visual Studio 2026.

## Project Setup

Target framework: `net10.0-windows`

```xml
<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>WinExe</OutputType>
    <TargetFramework>net10.0-windows</TargetFramework>
    <Nullable>enable</Nullable>
    <ImplicitUsings>enable</ImplicitUsings>
    <UseWPF>true</UseWPF>
  </PropertyGroup>
</Project>
```

## C# 14 New Language Features

### `field` keyword (backed properties)
Access the compiler-generated backing field inside a property accessor without declaring a separate field:

```csharp
public string Name
{
    get;
    set => field = value ?? throw new ArgumentNullException(nameof(value));
}
```

### Extension members
New `extension` block syntax supports extension properties (instance and static) in addition to extension methods:

```csharp
public static class MyExtensions
{
    extension(IEnumerable<int> source)
    {
        public bool IsEmpty => !source.Any();
    }
}
```

Use `sequence.IsEmpty` as if it were an instance property.

### Null-conditional assignment
`?.` can now appear on the left-hand side of an assignment:

```csharp
// Before C# 14:
if (customer is not null) customer.Order = GetCurrentOrder();

// C# 14:
customer?.Order = GetCurrentOrder();
```

Also works with compound assignment (`+=`, `-=`, etc.). Increment/decrement (`++`/`--`) are not supported.

### `nameof` with unbound generic types
```csharp
nameof(List<>)  // returns "List"
```

### Lambda parameter modifiers without explicit types
```csharp
TryParse<int> parse = (text, out result) => int.TryParse(text, out result);
```

### Implicit `Span<T>` / `ReadOnlySpan<T>` conversions
C# 14 adds first-class implicit conversions between `Span<T>`, `ReadOnlySpan<T>`, and `T[]`.

### `partial` constructors and events
Instance constructors and events can now be declared as `partial` members (one defining declaration, one implementing declaration).

### User-defined compound assignment and increment/decrement operators
Types can now define `+=`, `-=`, `++`, `--`, etc.

## WPF Changes in .NET 10

### Grid short-form syntax (new)
Column/row definitions can be written inline as a string:

```xaml
<!-- Before -->
<Grid>
    <Grid.ColumnDefinitions>
        <ColumnDefinition Width="1*" />
        <ColumnDefinition Width="Auto" />
        <ColumnDefinition Width="300" />
    </Grid.ColumnDefinitions>
</Grid>

<!-- .NET 10 -->
<Grid ColumnDefinitions="1*, Auto, 300" RowDefinitions="Auto, *, 25" />
```

### MessageBox new buttons and results (new)
`MessageBoxButton` now includes: `AbortRetryIgnore`, `RetryCancel`, `CancelTryContinue`.  
`MessageBoxResult` now includes: `Abort`, `Retry`, `Ignore`, `TryAgain`, `Continue`.

### Clipboard changes
WPF and Windows Forms now share the same clipboard API. `BinaryFormatter`-based clipboard methods are obsoleted; use JSON-based alternatives instead.

### Fluent style (in progress)
.NET 10 expanded Fluent UI style support to additional controls: `DatePicker`, `GridSplitter`, `GridView`, `GroupBox`, `Hyperlink`, `Label`, `NavigationWindow`, `RichTextBox`, `TextBox`.  
Fluent style support is still incomplete; not all controls are covered yet.

### Performance improvements
- Internal data structures replaced with `ReadOnlyCollection<T>` to reduce allocations.
- Optimized font rendering, dynamic resources, XAML parsing, and cache operations.

### Removed legacy code
Unused Code Access Security (CAS) code and XBAP-related code have been removed. Do not reference CAS APIs in .NET 10 WPF code.

## .NET 10 Runtime and SDK

- JIT: improved inlining, method devirtualization, and stack allocation optimization.
- AVX10.2 support added.
- NativeAOT enhancements.
- SDK: `dotnet test` now supports `Microsoft.Testing.Platform`; `dotnet tool exec` for one-shot tool execution.
- Post-quantum cryptography: ML-DSA with HashML-DSA support, Composite ML-DSA, AES KeyWrap with Padding.
- Networking: `WebSocketStream` API, TLS 1.3 on macOS.

## Guidance for Code Generation

- Always use `net10.0-windows` as the target framework for WPF projects.
- Use `<Nullable>enable</Nullable>` and `<ImplicitUsings>enable</ImplicitUsings>`.
- Prefer the `field` keyword instead of explicit backing fields for simple validation cases.
- Use the Grid inline syntax (`ColumnDefinitions="..."`) for conciseness.
- Do not use `BinaryFormatter` for clipboard operations; use the new JSON-based clipboard APIs.
- Do not reference CAS-related APIs (they have been removed).
- C# 14 is the default language version when targeting .NET 10; no explicit `<LangVersion>` needed.

## Reference Links

- [What's new in .NET 10](https://learn.microsoft.com/dotnet/core/whats-new/dotnet-10/overview)
- [What's new in C# 14](https://learn.microsoft.com/dotnet/csharp/whats-new/csharp-14)
- [What's new in WPF for .NET 10](https://learn.microsoft.com/dotnet/desktop/wpf/whats-new/net100)