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Span<T> and ReadOnlySpan<T>

4 posts

2026-11-07 csharp dotnet performance

How to loop over two variables in C# without allocating an array

foreach over (ReadOnlySpan<T>)[a, b] allocates nothing on .NET 8 and later and works for reference types, which stackalloc cannot do. On .NET 10 the compiler backs it with the BCL's InlineArray2<T>, and the JIT can even stack-allocate a plain new[] { a, b } once the method reaches Tier 1. Measured on .NET 10.0.10 and .NET 11 RC 3.

2026-10-30 comparison csharp dotnet

ref T loop vs Span<T> indexing in C#: why the span version is as fast or faster in .NET 10

On .NET 10 a plain for loop over span[i] bounded by span.Length compiles to a bounds-check-free, strength-reduced, down-counting loop. A hand-written Unsafe.Add(ref r, i) loop with an int index keeps a sign extension and an up-counting compare, and measured 2-5% slower. Benchmarks and JIT disassembly for arm64 and x64 on .NET 10.0.10.

2026-10-15 csharp csharp-14 dotnet-11

What Is ref-safe-context in C#, and How Does the Compiler Decide It for ref Locals?

Understand C# reference escape rules with compiler-checked examples for ref locals, reassignment, scoped references and heap-backed versus stack-backed spans.

2026-05-19 csharp-14 csharp dotnet-10

Fix: C# 14 overload resolution breaking change with Span and ReadOnlySpan

After upgrading to C# 14 / .NET 10, calls like array.Contains, x.Reverse(), and MemoryMarshal.Cast suddenly bind to different overloads or stop compiling. Here is what changed and how to pin the old behaviour where it matters.