Making foreach on an IEnumerable allocation-free using reflection and dynamic methods (andrewlock.net)

submitted 1 week ago by SmartmanApps@programming.dev to c/csharp@programming.dev

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[-] xianjam@programming.dev 2 points 1 week ago

Interesting stuff. I used to work under an engineer who was obsessed with performance tuning. I remember him converting all of our foreach loops to for loops. He probably told me, but I never knew/retained that it allocated on the heap. I also had always assumed reflection = slower.

Though, as he points out, .NET 10 does a similar kind of optimization for you. So, it seems like largely an unnecessary optimization. I can only imagine a 40-byte allocation optimization matters in an extremely low memory environment or at extreme scale.

[-] labsin@sh.itjust.works 2 points 4 days ago

In later .net version for loops can be slower than linq queries. If the compiler knows the iteration does not cause side effects, it often already does not allocate and can even vectorize some loops, so .Sum(...) might be faster then a manual for loop.

Optimizing without benchmarking is often wasted effort.

[-] xianjam@programming.dev 1 points 3 days ago

Funnily enough, that engineer also disallowed Linq because it was slow. It's been 7 years since I've worked with him. wonder if he ever changed his tune.