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Assigning values to class attributes in a list
f#testing

Hi,

I wonder if anyone might be able to help me out here.

I have a dll which exposes a class with various attributes. In a testing program written in F# I want to iterate through an array of GUI textboxes, assigning each value to the corresponding class attribute. So (in pseudo-F# code) I want to have something like.

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let myClass = new DLLClass()
let attributes = [myClass.a; myClass.b; myClass.c]

List.iteri (fun index attrib ->
                   attrib <- guibox.[index].Text
                   ) attributes

The problem I am having is that the value in 'attributes' is not mutable. I know this and I am not trying to mutate it but rather I'm trying to mutate the value it points to.
I have tried wrapping each attribute in ref(...) thinking I'd be creating a list of references to each attribute, but that doesn't work either.

Any help would be gratefully received.

Mark R

.

The problem is, that you copy the references (you might think the values) of the attributes to your list. So the entry in your list is not the setter of your class-attribute but a reference to it's value in memory.

You might try something like

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let attributes = [(fun s -> myClass.a <- s); (fun s -> myClass.b <- s); (fun s -> myClass.b <- s)]

and then just

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attributs |> List.iteri (fun index attrib -> attrib (guibox.[index].Text) )

I did not check if this works exactly this way, but it should (now the list is not of type (string list) but of type ((string -> unit) list) )

Of course you can think of some nicer syntax and/or using reflection ... have fun

By on 10/12/2010 2:09 AM ()

The problem is, that you copy the references (you might think the values) of the attributes to your list. So the entry in your list is not the setter of your class-attribute but a reference to it's value in memory.

You might try something like

1

let attributes = [(fun s -> myClass.a <- s); (fun s -> myClass.b <- s); (fun s -> myClass.b <- s)]

and then just

1

attributs |> List.iteri (fun index attrib -> attrib (guibox.[index].Text) )

I did not check if this works exactly this way, but it should (now the list is not of type (string list) but of type ((string -> unit) list) )

Of course you can think of some nicer syntax and/or using reflection ... have fun

I also think so.

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By on 11/4/2010 12:32 AM ()

Hi,

thanks for the quick reply.

I'm about to try your suggestion.

Regards

Mark

By on 10/12/2010 2:12 AM ()

Yes that seems to be working fine (I can't test it fully yet because I have a lot more to write but the compiler is happy now!).

It's actually quite straightforward now you've explained it.

(Assuming I'm reading this right)..
I have a list of functions which assign values to a specific attribute. I then iterate through that list applying each function to the respective textbox value.

By on 10/12/2010 2:27 AM ()

yep - that was the indent (of course you apply the textbox-text to the function but thats a minor detail ;)

By on 10/12/2010 2:29 AM ()

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