Tag: csharp

C# 15 adds the closed modifier in .NET 11 Preview 5, giving class hierarchies compile-time exhaustiveness in switch expressions. Here is how it works and the one gotcha.

A complete guide to CORS for a bearer-token API in ASP.NET Core 11: the correct UseCors ordering relative to authentication, why a bearer token in the Authorization header is not a CORS credential, why AllowAnyHeader works but a manual wildcard does not cover Authorization, and how to keep preflight from failing.

Seed the join table of a many-to-many relationship in EF Core 11: the implicit shadow keys you must name yourself, the UsingEntity HasData pattern, and the runtime UseSeeding alternative that works with skip navigations.

Seed reference data the right way in EF Core 11 with UseSeeding and UseAsyncSeeding: where to configure them, when they run, the idempotency check you cannot skip, and why you must implement both.

Span<T> is a stack-only ref struct that points at memory you already own, so it has no backing allocation. It speeds code up in exactly three situations: replacing a heap buffer with stackalloc, slicing without copying, and tight loops where the JIT elides bounds checks. Everywhere else it changes nothing, and across an await it does not compile.

DynamicallyAccessedMembers tells the .NET trimmer and AOT compiler which members of a Type you reach by reflection, so they are kept instead of trimmed away. It turns a silent runtime MissingMethodException into a build-time IL2070 warning. Here is what the attribute does, how the data-flow analysis behind it works, and how to annotate parameters, fields, and generic type parameters correctly.

ValueTask and ValueTask<T> are structs that let an async method return a result without heap-allocating a Task when it completes synchronously. The win is one fewer allocation on hot paths that usually finish without awaiting. The cost is a strict await-once contract. Here is what the type actually is, how it works, and the narrow set of cases where it earns its keep.

A plain-language guide to C# source generators: what they actually do, how the IIncrementalGenerator pipeline works, when they beat reflection or T4, and the cases where you should not reach for one. With runnable examples on .NET 11 and C# 14.

IAsyncEnumerable<T> is the interface for asynchronous streams: a sequence whose elements arrive over time and each one may require an await. Here is what it actually is, how await foreach and yield drive it, and the rule for when to reach for it over Task<List<T>>.

Native AOT compiles your .NET app to a single self-contained native binary with no JIT, buying fast startup and a small memory footprint. The price is a C toolchain at build time, slower publishes, per-RID builds, no reflection or Reflection.Emit, mandatory trimming, and no Dynamic PGO. Here is the full ledger.