[graboid]

I sometimes write C# in my day job. But I think I don't know much about how to write really fast C#. Do you have any recommendations for learning resources on that topic?

[gw2]

Sure. Here are some resources:

* Span<T>: https://learn.microsoft.com/en-us/archive/msdn-magazine/2018...

* C# now has a limited borrow checker-like mechanism to safely handle local references: https://em-tg.github.io/csborrow/

* Here is a series of articles on the topic: https://www.stevejgordon.co.uk/writing-high-performance-csha...

* In general, avoid enterprise style C# (ie., lots of class and design patterns) and features like LINQ which allocate a lot of temporaries.

[neonsunset]

LINQ is fine (but enterprise style never is, yes), it’s a matter of scale and what kind of a domain the code is targeted too. C# needs to be approached a little like C++ and Rust in this regard. Having standard performance optimization knowledge helps greatly.

Also can recommend reading all the performance improvements blog posts by Stephen Toub as well as learning to understand disassembly at a basic level which .NET offers a few convenient tools to get access to.

[graboid]

Thank you. I once read a bit about Span<T>, but some of this reference stuff is very new to me. Interesting, definitely. C# really is a big language nowadays...

[xigoi]

C# is specifically designed for enterprise-style OOP, so if you want to avoid that, why use C# at all?

[CrimsonCape]

Span<T>, ReadOnlySpan<T>, Memory<T>, CollectionsMarshal, CollectionsExtensions, ref struct, ref return, ArrayPool, ArraySegment, ValueTuple, and using interfaces/structs/generics carefully.

That is if you don't want to get into unsafe code.

[HackerThemAll]

A few important ones: - Avoid memory allocations as much as you can. That's a primary thing. For example, case insensitive string comparisons using "a.ToUpper() == b.ToUpper()" in a tight loop are a performance disaster, when "string.Equals(a, b, StringComparison.CurrentCultureIgnoreCase)" is readily available. - Do not use string concatenation (which allocates), instead prefer StringBuilder, - Generally remember than any string operation (such as extracting a substring) means allocation of a new string. Instead use methods that return Span over the original string, in case of mystr.Substring(4,6) it can be a.AsSpan(4,6), - Beware of some combinations of Linq methods, such as "collection.Where(condition).First()" is faster than "collection.First(condition)" etc.

Apart from that (which simply concerns strings, as they're the great source of performance issues, all generic best practices, applicable to any language, should be followed.

There are plenty resources on the net, just search for it.