Use of the `_.Property` shorthand in delegates

[lucasteles]

I propose we enable to use of the new _.Property shorthand for accessor within Func<> and Expression<Func<>> as normal lambdas

["foo"; "42"; ""] |> List.map _.Length // [3; 2; 0]

open System.Linq
["foo"; "42"; ""].Select(_.Length) // fail

The existing way of approaching this problem in F# is:

Using normal lambdas

["foo"; "42"; ""].Select(fun s -> s.Length) 

Pros and Cons

The advantages of making this adjustment to F# are : make the syntax consistent

The disadvantages of making this adjustment to F# are : N/A

Extra information

Estimated cost (XS, S, M, L, XL, XXL):

Related suggestions: https://github.com/fsharp/fslang-suggestions/issues/506

Affidavit (please submit!)

Please tick these items by placing a cross in the box:

• [x] This is not a question (e.g. like one you might ask on StackOverflow) and I have searched StackOverflow for discussions of this issue
• [x] This is a language change and not purely a tooling change (e.g. compiler bug, editor support, warning/error messages, new warning, non-breaking optimisation) belonging to the compiler and tooling repository
• [x] This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it
• [x] I have searched both open and closed suggestions on this site and believe this is not a duplicate

Please tick all that apply:

• [x] This is not a breaking change to the F# language design
• [ ] I or my company would be willing to help implement and/or test this

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[lucasteles]

cc @vzarytovskii

[Happypig375]

["foo"; "42"; ""].Select(_.Length) :x: ["foo"; "42"; ""].Select _.Length ✔️

[lucasteles]

@Happypig375 I believe both should work, the first is important to not break the fluent chain

["foo"; "42"; ""].Select(_.Length).Where(isEven)

[Happypig375]

@lucasteles only needed when there is a fluent chain.

[cmeeren]

This already has an issue: #506

Edit: Oh wait, is this specifically for Func/Expression?

[Happypig375]

@cmeeren This is for any delegate, not F# function types.

[cmeeren]

Yes, then I definitely second this.

[T-Gro]

This was done as part of https://github.com/dotnet/fsharp/pull/16339 (it is in main, not yet in the released product) The following three syntax options of doing the same now work, does it cover all of this suggestion?

open System.Linq
let _ = [""; ""; ""].Select(fun x -> x.Length)
let _ = [""; ""; ""].Select(_.Length)
let _ = [""; ""; ""].Select _.Length

[cmeeren]

From what I can see, this would fix the issue, though I'm not the OP.

[abelbraaksma]

Works like a charm (in main)!