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Implementing an interface method with out parameter
f#

hello,

this may be easy to solve or was answered before, but i cant find a solution by search.
I have to implement a method from an interface which has an integer out paramater. VS 2010 tells me its an byref<int> type so i though i could write something like this:

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let getTex forPin onDevice (texturePointer:int byref) =
        texturePointer <- 0
        if forPin = myTextureOut then
            let t = FDeviceTextures.[onDevice]
            if not (t = null) then
                texturePointer <- t.ComPointer.ToInt32()

interface IPluginDXTexture with
        member this.GetTexture(forPin, onDevice, texturePointer) = getTex forPin onDevice texturePointer

But here VS says for the argument texturePointer:
Error 1 This expression was expected to have type byref<int> but here has type int

So I tried passing &texturePointer or (ref texturePointer) but it didnt work.. I always get a type error

Thanks for any hint!

.

As you say, you need to use &arg at any byref call site.

I also see that if the 'let' is bound inside a class it does not work (I'm unsure why offhand), but moving it outside the class to module scope works:

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type IFoo =
    abstract Foo : x:int * y:int byref -> int

// does work to define 'let' at module scope
let impl(x:int, y:int byref) : int =
    y <- x
    x + 1

type MyFoo() =
// does not work to define this inside a class and try to call it
//    let impl(x:int, y:int byref) : int =
//        y <- x
//        x + 1

    let impl2(x:int, y:int byref) : int =
        impl(x, &y)
        
    member this.Bar(x:int,y:int byref) = 
        let z = y
        printfn "%d" z
        impl(x,&y)

    interface IFoo with
        member this.Foo(x:int,y:int byref) = 
            impl(x,&y)
By on 3/29/2010 5:56 PM ()

ok, this sounds like a bug, i see no resaon why this should not be possible..

I can confilm, that it works when i move the function out of the class into a common module. but this is no solution for me, since i have to use class members in that function.

maybe it works as a member function instead of a let binding of the class.. i try that.

By on 3/29/2010 6:15 PM ()

yea, that was the solution, it works as a member function of the class, but only with a tuple argument..

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member this.getTex (forPin, onDevice, texturePointer:int byref) =
        texturePointer <- 0
        if forPin = myTextureOut then
            let t = FDeviceTextures.[onDevice]
            if not (t = null) then
                texturePointer <- t.ComPointer.ToInt32()


interface IPluginDXTexture with
        member this.GetTexture(forPin, onDevice, texturePointer) = this.getTex (forPin, onDevice, &texturePointer)

strage, i still believe its a bug..

thanks for the fast answer!

By on 3/29/2010 6:33 PM ()

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