F# list to C# IEnumerable: most efficient method?

Question

I'm currently working on an F# library with GUI written in C# and I would like to ask what is the best or correct way to pass an F# (generic) list to a C# code (generic IEnumerable).

I've found three ways so far:

[1; 2; 3; 4; 5;] |> List.toSeq

[1; 2; 3; 4; 5;] |> Seq.ofList 

[1; 2; 3; 4; 5;] :> seq<int>

Is there any practical difference between these three methods, please?

Arbitration

Answer 1

If you look in the F# library source code, you'll find out that they are all the same:

• Seq.ofList just calls List.ofSeq as you can see here in the "list.fs" file

• List.toSeq is implemented using s :> seq<_> as you can see here in the "seq.fs" file

In terms of readability, I would probably use Seq.ofList or List.toSeq, especially if the code is a part of a larger F# pipeline, because then it makes the code a bit nicer:

someInput
|> List.map (fun x -> whatever) 
|> List.toSeq

Avowed

To expand a bit on Tomas's excellent answer: my general recommendation on whether to use Seq.ofList or List.toSeq would be to ask yourself "What is my code using?" If (as in this example) you have a list and you want to produce a seq/IEnumerable for other code to consume, then use List.toSeq. If you have received a list and you want to get a seq for your own code to consume, use Seq.ofList. In other words, pick the function that most matches the "direction" of data flow in this particular part of your code. – Naima

If you nuget FSharp.Core.Fluent you will be able to dot into the list like: [1;2;3].toSeq(). – Debrief