使用F＃类型提供程序实例化类型并将其显示为属性

Question

I'd like to do the following:

let allTypes = AllTypes (t, assemblies)

... where AllTypes is a type provider, the properties of which are instances of all types in the given array of assemblies that subclass type t . (All of the types have a single constructor that takes no arguments.)

Is this doable using F# type providers? I have no experience creating my own provider, and I don't want to waste my time attempting to do this if it isn't feasible.

I'd greatly appreciate any links to pages that would get me started coding this.

Answer 1

You don't need a type provider for that; you can write that code using basic reflection:

open System.Reflection

let allTypes (baseClass : Type) (assemblies : Assembly seq) =
    assemblies
    |> Seq.collect (fun x -> x.GetExportedTypes())
    |> Seq.filter (fun x -> baseClass.IsAssignableFrom x)
    |> Seq.collect (fun x -> x.GetConstructors())
    |> Seq.filter (fun x -> x.GetParameters().Length = 0)
    |> Seq.map (fun x -> x.Invoke([||]))

The allTypes function has this signature: Type -> Assembly seq -> obj seq .

Answer 2

there's a lot of activity going on in the FSharp.Data github repo. There is a learning curve, but tuning into that repo might be useful.

Beyond that, this intro tutorial covers some of the basics, and here's a Type Provider starter pack that's been prepared by the F# open source community.

The fsharp.org site, and this projects page covers a cross-section of what's going on (including type providers).

You could take the list that Mark suggests here and turn it into a type provider. I think an exploratory way of interacting with namespaces would be useful. Why not? I'd use it. Please publish on GitHub if you get around to it.