CODEWITHSUNDEEP
syntaxf#constructorpipe
gradbot
gradbot

Reputation: 13862

Using the F# pipe symbol with an object constructor

I'm trying to figure out the correct syntax to use the pipe operator |> into the creation of an object. Currently I'm using a static member to create the object and just piping to that. Here is the simplified version.

type Shape = 
    val points : Vector[]

    new (points) =
        { points = points; }

    static member create(points) =
        Shape(points)

    static member concat(shapes : Shape list) =
        shapes
            |> List.map (fun shape -> shape.points)
            |> Array.concat
            |> Shape.create

What I want to do ...

    static member concat(shapes : Shape list) =
        shapes
            |> List.map (fun shape -> shape.points)
            |> Array.concat
            |> (new Shape)

Is something like this possible? I don't want to duplicate code by repeating my constructor with the static member create.

Update Constructors are first-class functions as of F# 4.0

In F# 4.0 the correct syntax is.

    static member concat(shapes : Shape list) =
        shapes
            |> List.map (fun shape -> shape.points)
            |> Array.concat
            |> Shape

Upvotes: 16

Views: 2522

Answers (2)

MichaelGG
MichaelGG

Reputation: 10006

Apparently, object constructors aren't composable. Discriminated union constructors don't seem to have this problem:

> 1 + 1 |> Some;;
val it : int option = Some 2

If you want to use the pipeline, Brian's answer is probably best. In this case, I'd consider just wrapping the entire expression with Shape( ).

Upvotes: 3

Brian
Brian

Reputation: 118915

There's always

(fun args -> new Shape(args))

Upvotes: 19

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