Implicit conversion to discriminated union

SRTP and active patterns tricks for mimicking Typescript union types

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// Caution!
// Don't use in real code.

module Domain =
    type UnionType = 
        | Int of int
        | Long of int64
        | String of string
    with
        static member ($) (UnionType, x:int) = Int(x)
        static member ($) (UnionType, x:int64) = Long(x)
        static member ($) (UnionType, x:string) = String(x) 

    let inline (|UnionType|) x = Unchecked.defaultof<UnionType> $ x

open Domain

let show x = 
  match x with
  | Int x -> printfn "int: %d" x
  | Long x -> printfn "long: %d" x
  | String x -> printfn "string: %s" x

let inline showImplicit (UnionType x) = show x

showImplicit "Hello world!"

type UnionType =
  | Int of int
  | Long of int64
  | String of string
  static member ( $ ) : UnionType:'a * x:int -> UnionType
  static member ( $ ) : UnionType:'a * x:int64 -> UnionType
  static member ( $ ) : UnionType:'a * x:string -> UnionType

Full name: Script.Domain.UnionType

union case UnionType.Int: int -> UnionType

Multiple items
val int : value:'T -> int (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int

--------------------
type int = int32

Full name: Microsoft.FSharp.Core.int

--------------------
type int<'Measure> = int

Full name: Microsoft.FSharp.Core.int<_>

union case UnionType.Long: int64 -> UnionType

Multiple items
val int64 : value:'T -> int64 (requires member op_Explicit)

Full name: Microsoft.FSharp.Core.Operators.int64

--------------------
type int64 = System.Int64

Full name: Microsoft.FSharp.Core.int64

--------------------
type int64<'Measure> = int64

Full name: Microsoft.FSharp.Core.int64<_>

Multiple items
union case UnionType.String: string -> UnionType

--------------------
module String

from Microsoft.FSharp.Core

Multiple items
val string : value:'T -> string

Full name: Microsoft.FSharp.Core.Operators.string

--------------------
type string = System.String

Full name: Microsoft.FSharp.Core.string

Multiple items
val UnionType : 'a

--------------------
type UnionType =
  | Int of int
  | Long of int64
  | String of string
  static member ( $ ) : UnionType:'a * x:int -> UnionType
  static member ( $ ) : UnionType:'a * x:int64 -> UnionType
  static member ( $ ) : UnionType:'a * x:string -> UnionType

Full name: Script.Domain.UnionType

val x : int

val x : int64

val x : string

val x : 'a (requires member ( $ ))

module Unchecked

from Microsoft.FSharp.Core.Operators

val defaultof<'T> : 'T

Full name: Microsoft.FSharp.Core.Operators.Unchecked.defaultof

module Domain

from Script

val show : x:UnionType -> unit

Full name: Script.show

val x : UnionType

val printfn : format:Printf.TextWriterFormat<'T> -> 'T

Full name: Microsoft.FSharp.Core.ExtraTopLevelOperators.printfn

val showImplicit : 'a -> unit (requires member ( $ ))

Full name: Script.showImplicit

Multiple items
active recognizer UnionType: 'a -> '_arg3

Full name: Script.Domain.( |UnionType| )

--------------------
type UnionType =
  | Int of int
  | Long of int64
  | String of string
  static member ( $ ) : UnionType:'a * x:int -> UnionType
  static member ( $ ) : UnionType:'a * x:int64 -> UnionType
  static member ( $ ) : UnionType:'a * x:string -> UnionType

Full name: Script.Domain.UnionType

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More information

Link:	http://fssnip.net/7SO
Posted:	6 years ago
Author:	Evgeniy Andreev
Tags:	#srtp , #active patterns