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Using IDesign ServiceModelEx InProcFactory.CreateInstance<S, I>()
f#

I want to create a service using IDesigns InProcFactory with the following statement

let service = InProcFactory.CreateInstance<ControlNumberGenerationService, IGenerateControlNumber>()

(This post will not show this function correctly. The generics are S=ControlNumberGenerationService and I=IGenerateControlNumber)

I am getting this error:

Error 1 This expression was expected to have type ControlNumberGenerationService but here has type IGenerateControlNumber.

This call works correctly in C#...does anyone know what the difference is?

.

By any chance, is there a "naked type constraint" on CreateInstance (i.e. is the signature actually 

1

CreateInstance<S,I>() where S : I

)? If so, it's unfortunately not possible to call the method in F# unless S and I are the exact same type.

By on 12/7/2010 1:45 PM ()

There is a "where" clause on this method. S is equal to the service being called and I equals the interface the service implements.

That answers why it compiles when I change both to one value.

Are there any workarounds?

By on 12/8/2010 6:57 AM ()

There is a "where" clause on this method. S is equal to the service being called and I equals the interface the service implements.

That answers why it compiles when I change both to one value.

Are there any workarounds?

Sadly, there's no good workaround. One option would be to write a C# shim which creates and wraps that object (but the C# object you expose would need not to have multiple type parameters which have a subtype relationship). Another option would be to create the object in F# using reflection (and store it as a variable of type obj) and then call any methods on it reflectively as well (possibly using the F# (?) operator to simplify the syntax).

By on 12/8/2010 7:50 AM ()

Assuming that, in this case, CreateService<S,S> returns the same object as CreateService<S,I> (does it?), why not just call CreateService<S,S> :> I e.g. call it and then upcast to the target interface?

By on 12/8/2010 8:03 AM ()

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