mutable fields in Structs are not described

[Szer]

Documentation lacks examples of
val mutable fields and way of their mutation without implicit copying of structure.

[<Struct>]
type Foo = 
  val mutable bar: string
  member self.ChangeBar bar = self.bar <- bar
  new (bar) = {bar = bar}

let foo = Foo "1"
foo.ChangeBar "2" //make implicit copy of Foo, changes the copy, discards the copy, foo remains unchanged
printfn "%s" foo.bar //prints 1

let mutable foo' = Foo "1"
foo'.ChangeBar "2" //changes foo'
printfn "%s" foo'.bar //prints 2

---

Document Details

⚠ Do not edit this section. It is required for docs.microsoft.com ➟ GitHub issue linking.

• ID: 9a067d5a-bb13-9991-c808-c7c49a00ca47
• Version Independent ID: 201272a0-3350-93f3-8965-4a745671c7e7
• Content: Structures (F#)
• Content Source: docs/fsharp/language-reference/structures.md
• Product: dotnet-fsharp
• GitHub Login: @cartermp
• Microsoft Alias: phcart

[cartermp]

Mutable fields in structs are described here: https://docs.microsoft.com/en-us/dotnet/fsharp/language-reference/members/explicit-fields-the-val-keyword

However, gotchas around implicit copies (such as your example) are not documented. Would you be willing to submit a PR to the structures file that explains this? I can put it on my backlog but there's no guarantee it'll be done soon.

[Szer]

@cartermp
PR for docs
#9695
PR for snippets
dotnet/samples#531

[cartermp]

Thanks a bunch @Szer