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Conversion between a class/type and a record
f#

Hi,

I'm extremely new to F#. I'm trying to convert between an record and a class (the class is actually defined in a C# assembly):

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module Brands =
 
    type BrandModel = { mutable Id: int; mutable name: string; mutable disabled: bool; }
 
    let toD model : 'T =
        match box model with            
            | :? BrandModel -> 
                Mapper.CreateMap<BrandModel, Brand>() |> ignore
                Mapper.Map<BrandModel, Brand>(model) :?> 'T
 
            | :? IEnumerable<BrandModel> as models -> 
                Mapper.CreateMap<IEnumerable<BrandModel>, IEnumerable<Brand>>() |> ignore
                Mapper.Map<IEnumerable<BrandModel>, IEnumerable<Brand>>(models) :?> 'T
 
            | _ -> Unchecked.defaultof<'T>
 
    let toM domain : 'T =
        match box domain with
            | :? Brand ->
                Mapper.CreateMap<Brand, BrandModel>() |> ignore
                Mapper.Map<Brand, BrandModel>(domain) :?> 'T
 
            | :? IEnumerable<Brand> as domains ->
                Mapper.CreateMap<IEnumerable<Brand>, IEnumerable<BrandModel>>() |> ignore
                Mapper.Map<IEnumerable<Brand>, IEnumerable<BrandModel>>(domains) :?> 'T
 
            | _ -> Unchecked.defaultof<'T>

The error I'm getting is: Error    1    The type 'BrandModel' does not have any proper subtypes and cannot be used as the source of a type test or runtime coercion.    C:\Working\AdminConsoleV2\Models\BrandModel.fs    29    17    Models

What I understand from the error is that I'm trying to downcast from Brand to BrandModel, yet BrandModel is a record, and therefore can't use inheritance, and therefore can't be downcasted.

1. Is my understanding of the problem correct?
2. Is it possible to cast a class to a record?
3. How can I rewrite the above two functions? Their purpose is to convert from Brand to BrandModel and back. Each function should take care of converting a single object and a collection of objects.

.

Hi, Jacques!
I can't figure out what part of code compiler considers to be the error. You must also specify the return type of Mapper.Map function (or constructor) so I can understand your code. Also, this code works:

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match box model with            
    | :? BrandModel -> 
        ()
 
    | :? IEnumerable<BrandModel> as models -> 
        ()
 
    | _ -> Unchecked.defaultof<'T>

which makes me think that you use incorrect cast direction to 'T. Are you sure you want to dowcast result, rather than upcast it?

By on 10/3/2011 2:18 AM ()

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