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How does Memory<T> differ from Span<T>, and when would you use Memory<T> instead? How do you slice an array or string efficiently without allocating a new array/string, using Span<T> or ReadOnlySpan<T>? What restrictions does the C# compiler enforce on Span<T> because it's a 'ref struct'? How does 'stackalloc' work together with Span<T> to allocate memory on the stack instead of the heap? How does the modern .NET Span-based string.Split (via MemoryExtensions) or manual span-splitting reduce garbage collection pressure compared to string.Split()? How would you use Span<T> to implement an in-place array reversal or sorting algorithm without allocating a temporary array? What is the role of Span<T> and Memory<T> in .NET, and why can't Span<T> be used inside an async method?
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How would you write a high-performance CSV field parser using ReadOnlySpan<char> that avoids all intermediate string allocations?

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Answer

Use ReadOnlySpan<char>.IndexOf() or Split-style enumeration to locate delimiters directly within the original string's span, slicing out each field as its own ReadOnlySpan<char> — only convert a field to an actual 'string' (via .ToString()) at the very last moment when you genuinely need to store or return it as a heap-allocated string.
ReadOnlySpan<char> line = "Sam,30,Engineer".AsSpan();
int firstComma = line.IndexOf(',');
ReadOnlySpan<char> name = line.Slice(0, firstComma); // no allocation yet
ReadOnlySpan<char> rest = line.Slice(firstComma + 1);
// ... continue slicing 'rest' for remaining fields
Real-world example Parsing millions of lines of a large CSV or log file in a batch job where allocation overhead directly impacts throughput.

Common follow-ups: At what point in this pipeline would you actually be FORCED to allocate a real string?

String Handling & StringBuilder
All 11 Arrays, Span<T> & Memory<T> questions