What's new in .NET 9 & C# 13
summary
.NET 9 ships concrete changes: induction variable widening gives 64-bit loops measurable speedups simply by recompiling; new Span-friendly APIs (Base64Url, file helpers, span Split) cut allocations; System.Text.Json gains indentation, respect nullable and constructor-respect options for stricter deserialization; ASP.NET Core adds pushed authorization requests (reduces URL leakage), built-in OpenAPI (replaces Swashbuckle), map static assets and analyzers that catch AllowAnonymous/Authorize mistakes; a hybrid cache (memory + distributed) works and simplifies caching; .NET Aspire runs multi-service dev environments in Docker with a working dashboard; C# 13 previews include the field keyword and params collections.
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chapters (22)
- 0:00.NET 9 & C# 13 intro
- 2:30Why update to .NET 9
- 7:04Performance in .NET 9
- 9:31Spans and memory in .NET 9
- 13:42Feature switches & trimming
- 16:29System.Text.Json updates
- 20:19File & span API enhancements
- 24:36TimeSpan & security updates
- 25:39ASP.NET Core 9 security
- 27:25OpenAPI & Swashbuckle replacement
- 28:52Static assets & analyzers
- 30:38Minimal API improvements
- 32:03Hybrid caching in .NET 9
- 35:19.NET Aspire intro
- 41:43Debugging & telemetry
- 44:13Blazor & MAUI updates
- 44:55C# 13 new features
- 47:21Implicit index access
- 50:14Params collections
- 52:00Field keyword & breaking changes
- 56:34Future of C# & async
- 59:25Conclusion & resources
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