[RFC FS-1098] "Inline if lambda" attribute on function parameters of inline functions

[dsyme]

Discussion thread for RFC FS-1098 Inline if lambda attribute

[Tarmil]

Will this also allow capturing byref types in the lambda? For example allowing something like this if Array.iteri had this attribute:

let copy (source: int[]) (target: Span<int>) =
    source |> Array.iteri (fun i x -> target.[i] <- x)

[baronfel]

Excellent question! I know there have been other language suggestions around making core library functions work with byreflike parameters, perhaps this would be an alternative pathway to enabling that?

[dsyme]

Yes, I have just added the ability to use this attribute on F#-defined delegate types, which can accept byrefs.

The optimizer know knows how to online and reduce invokes on these.

I will update the RFC tomorrow or Tuesday

[dsyme]

(F# functions can't accept byref parameters due to limitations of dotnet generics. But delegate type can if part of their signature )

[dsyme]

This works well for computation expressions, but may be awkward for bloke the above, since it may need new delegate type definition. It is what it is.

[krauthaufen]

Hey, I would have needed this quite often and the workarounds most often turned out to be code-duplication and less abstraction, so I would love to see that happen.

I was wondering why we can't just inline all lambdas in functions being inline themselves when there is only one (syntactic) invocation? This rule would ensure that the code-size keeps small and cover a lot of cases.

[dsyme]

It's a good question. I don't have a good answer :)