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C# Feature - Implicit Span and ReadOnlySpan conversions

Implicit Span and ReadOnlySpan conversions

C# 14 adds more implicit conversions involving Span<T>, ReadOnlySpan<T>, and arrays so span-based APIs compose more naturally.

Introduced In

This feature was introduced in C# 14. The official Microsoft Learn page for C# 14 is dated November 18, 2025 and states that C# 14 ships with .NET 10 and Visual Studio 2026.

Why This Feature Exists

Span-based APIs are common in modern high-performance .NET code. Earlier language versions already supported spans, but some common conversions still felt more manual than they should. C# 14 improves ergonomics so APIs using spans participate more smoothly in extension calls, overload resolution, and generic inference.

Example

static void Print(ReadOnlySpan<char> value)
{
  Console.WriteLine(value.ToString());
}

char[] buffer = ['O', 'K'];
Print(buffer);

When To Use It

Use it when designing or consuming APIs that prefer spans over arrays or strings for performance reasons.
Expect the biggest benefit in parsing, encoding, serializers, protocol handlers, and tight loops.

Common Pitfalls

Better conversions do not change span lifetime rules.
Readability still matters; span-heavy APIs should be used when performance is actually relevant, not by default everywhere.