Is F# slower than C#

[Xyncgas]

List is a feature that use linked list
tuples are not value types by default let k = (3,2) //unless let k = struct (3,2)
lambdas are not inlined if you use the >> operator to chain it to another function

[abelbraaksma]

About your last statement: ‘it depends’, but since the concept doesn’t exist in C#, there’s no comparison for >>.

And yes, a list is a linked list, and as linked lists go, it’s about the fastest in .NET. You could build a linked list in C#, but it’ll likely be slower. Don’t confuse it with System.Collections.Generic.List, which is ResizeArray in F#, and has nothing to do with a linked list.

A reference tuple is the same as the Tuple type in C#. No difference there, but F# is smart enough to optimise it away in function applications, method invocations and a lot more. There’s no inherent difference in speed between a ref tuple and a struct tuple, the modifier merely changes the internal representation. Depending on your data, it can be faster or slower. Again, the same in C# with struct and class differences (heap vs stack alloc).

Since the compiled code is Common IL, there’s no inherent performance difference. There are, however cases where F# does optimisations you won’t find in C# (source inlining, SRTP, tailcalls) and vv, C# does optimisations you won’t find in F#.

In the end, any high performant C# code can be translated to high performant F# code. They all use the same BCL, and the same Common IL and CLI. In some aspects, F# can be more performant, because it has more static knowledge of types (like type erasure, currently only on tuples, option v nullables, type alias and UoM). However, not all such optimisations are currently implemented. Though, even with that, since all target the same infra, there won’t be anything that cannot be expressed in the other language.

If you have a concrete example of some code that you deem slower than its C# equivalent, feel free to share.

[vzarytovskii]

I, once again, suggest asking such questions either on SO (bigger audience), or over at https://github.com/dotnet/fsharp/discussions/categories/q-a, since it usually have more people paying attention to it.
This repo is generally for language suggestions and related discussions, and generally have less people following it.