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Using a function as a custom attribute value
f#

I'm trying to use a function as a custom attribute value, but I am getting the error:

error: invalid custom attribute value (not a constant): func.

Is this not supported, or possibly a .NET restriction?

Here is my sample code:

type TestFunctionType = int -> bool

type TestAttribute(func: TestFunctionType) =
inherit Attribute()
member this.Func = func

let func x = x > 2

type TestRecord = {
[<Test(func)>] aMember: int
}

Thanks
Howard

.

You can't use a function as an attribute property, only primitive types (int, string, etc.) and System.Type. It's a .NET restriction.

By on 3/18/2008 4:18 PM ()

Thanks for the response.

I worked around it by using a type which I expect to have some certain constructor types and a certain method on it. Not ideal for what I want to do but it basically works.

As some background, this is essentially an extension to the schema compiler type approach from the Expert F# book. A record describes a data format extracted from an external source, with attributes describing where to get the data from. But in some cases I want to supply a data converter function that converts the data from the external source into the data I want to store in the record. So I would like to be able to supply this function in the attribute.

By on 3/19/2008 7:19 PM ()

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