Generated type provider: extended sample
Can I create a generated type provider that provides types that are equivalent to the following F # code?
[<ProvidedTypeFlag("myTypeA")>]
type A(x:int) =
inherit ValueType(x)
member __.X = x+1
[<ProvidedTypeFlag("myTypeB")>]
type B(value:ValueType) =
member __.Raw = value
member __.toA = A(value.X)
interface IComparable with
member this.CompareTo obj =
match obj with
| :? B as other -> this.Raw.X.CompareTo (other.Raw.X)
| _ -> invalidArg "obj" "not a B"
[<ProvidedTypeFlag("myTypeC")>]
type C() =
static member Process(a:A) =
seq {
for x in [1..a.X] do
yield B(ValueType(x))
} |> Set.ofSeq
suppose i have the following types in the same assembly
// Value type that hold some data from 3rd party system
type ValueType (x:int) =
member __.X = x
// Custom attribute that I want to have on provided types
[<AttributeUsage(AttributeTargets.Class, AllowMultiple=false)>]
type ProvidedTypeFlagAttribute(originName:string) =
inherit System.Attribute()
member __.OriginName = originName
If possible please provide an example on how to do this using ProvidedTypes.fs
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Looking at this, it looks like you need a few small pieces.
Add custom attribute
I am using a little helper like this:
type CustomAttributeDataExt =
static member Make(ctorInfo, ?args, ?namedArgs) =
{ new CustomAttributeData() with
member __.Constructor = ctorInfo
member __.ConstructorArguments = defaultArg args [||] :> IList<_>
member __.NamedArguments = defaultArg namedArgs [||] :> IList<_> }
The optional arguments args and namedArgs look a little simpler and also a code cleaner. When I want to add a custom attribute, if there are more than one, I usually add a few more typed helpers to make the code clearer in code:
module Attributes =
let MakeActionAttributeData(argument:string) =
CustomAttributeDataExt.Make(typeof<ActionAttribute>.GetConstructor(typeof<string>),
[| CustomAttributeTypedArgument(typeof<ActionAttribute>, argument) |])
open Attributes
myProperty.AddCustomAttribute <| Attributes.MakeActionAttributeData("attributeData")
Adding a Constructor Calling the Base Type
Again, I have some helpers to think about:
type Type with
member x.GetConstructor(typ) =
x.GetConstructor([|typ|])
member x.TryGetConstructor(typ:Type) =
x.GetConstructor(typ) |> function null -> None | v -> Some v
...
create your provided type as usual (remember to set IsErased = false) then
//string ctor
match providedType.TryGetConstructor(typeof<string>) with
| None -> failwithf "No string constructor found for type: %s" providedType.Name
| Some ctor -> let stringCtor = ProvidedConstructor([ProvidedParameter("theString", typeof<string>)], InvokeCode=Expr.emptyInvoke, BaseConstructorCall = fun args -> ctor, args)
providedController.AddMember(stringCtor)
I think other parts should be documented elsewhere, especially with the addition of regular members, etc.
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