ValueOption parity with options

[cartermp]

Title of Suggestion

I propose we:

• Add equivalent module-bound functions for ValueOption so that it has parity with regular options.
• Add further properties to the ValueOption type to match what exists in Option
• Add the same debugger display as options

The existing way of approaching this problem in F# is to write these functions and/or type extensions yourself.

Pros and Cons

The advantages of making this adjustment to F# are:

• Makes ValueOption feel more first-class
• Resolves an awkwardness where there is a lot more utility with the Option type than the ValueOption type

The disadvantages of making this adjustment to F# are:

• It's more API surface area to build and test
• If we ever add some way to write code that is generic over "option-shaped" types, we'll have needless code duplication

Extra information

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

Related suggestion: #612

Affidavit (please submit!)

Please tick this by placing a cross in the box:

• This is not a question (e.g. like one you might ask on stackoverflow) and I have searched stackoverflow for discussions of this issue
• I have searched both open and closed suggestions on this site and believe this is not a duplicate
• 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.

Please tick all that apply:

• 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

[cartermp]

Approving as per "703 seems OK to do" from @dsyme in slack 🙂

[cartermp]

Closing this out as it is committed and shipping: https://github.com/fsharp/fslang-design/blob/master/FSharp.Core-4.6.0/FS-1065-valueoption-parity.md

[Thorium]

What is the preferred way to map option to value-option? With lists there are Seq.toList and Map.ofArray etc but I can't see ValueOption.ofOption or Option.ToValueOption or anything like that.

Just match x with Some v -> ValueSome v | None -> ValueNone everywhere?

And different kind of tryFinds will be composed with >> function Some x -> ValueSome x | None -> ValueNone ?

[brianrourkeboll]

I'll just note here for posterity that #703 (comment) was addressed via an addendum to the RFC for this feature in fsharp/fslang-design#779, implemented in dotnet/fsharp#17436.