Key Techniques

1. Pass by Reference: Use ref and in parameters for structs to avoid copying.
2. Return Span<T>: Instead of string.Substring() or List<T>, return slices of the original data.
3. Allocation-Free Iterators: Implement GetEnumerator() as a ref struct to avoid boxing in foreach.

Example: Allocation-Free Parsing

csharp public static bool TryParseInt(ReadOnlySpan<char> input, out int result) { // Parsing directly into Span, without creating intermediate strings }

Measuring Efficiency

Use BenchmarkDotNet with MemoryDiagnoser. The goal is Allocated = 0 per operation. Note that the JIT may inline small methods, but Span can sometimes prevent inlining due to ref struct constraints.

Trade-off: Allocation-free code is harder to read and maintain. Use it only after profiling, when allocations are proven to be a bottleneck.