Created
December 1, 2018 13:58
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| open Microsoft.FSharp.Quotations.Patterns | |
| open System.Reflection | |
| let nullTraverse<'a> (expr: Quotations.Expr<'a>) (originObj : obj) : 'a option = | |
| let inline tryGet (p : PropertyInfo) o = | |
| p.GetMethod.Invoke(o,null) | |
| |> Option.ofObj | |
| let rec innerTraverse (nullableObj : obj) = function | |
| | PropertyGet(None, props, _) -> tryGet props obj | |
| | PropertyGet(Some expr, props, _) -> | |
| innerTraverse nullableObj expr | |
| |> Option.bind (tryGet props) | |
| | _ -> failwithf "only get properties are allowed in null traverse" | |
| innerTraverse originObj expr | |
| |> Option.map (fun x -> (x :?> 'a)) | |
| let (|NullTraverse|_|) = nullTraverse | |
| type C = { C : obj } | |
| type B = { B : string } | |
| type A = { A : B } | |
| let a = {A = { B = null}} | |
| match a with | |
| | NullTraverse <@a.A.B@> x -> printfn "not null: %A" x | |
| | _ -> printfn "null" |
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