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Code simplification question
f# plugin
Hi All,

I'm still working on a plugin manager, and have a question about the following function. Basically, this function takes in a type t and a plugin manager mgr. It goes through each types within each assembly loaded into the manager, and creates an instance should the desired type be in the assembly type's inheritance tree. Now, the reason I added in a parameter 'a is so that I can return a seq<'a> instead of just seq<obj>.

So, my question is, are both parameters required or is there a way to simplify this function?

let create<'a> t (mgr: PluginManager) =
  { for x in assemblies mgr
    for y in HA.types x
    when Helper.is_a t y
    -> (HA.domain x).
         CreateInstanceAndUnwrap((HA.assembly x).FullName, y.FullName) }
  |> Seq.map (function :? 'a as z -> z)

Thanks and regards,

z.
.
You can simplify the function by removing the map and adding a dynamic downcast to 'a in the return expression of the seq comprehension.

Whether both parameters are required really depends on how you want to use this function. My guess is that both 'a and t are meant to refer to the same type, this type is statically known, it is an interface or abstract class, and implementations of it will be found in the plugin assemblies. In which case you can remove the t parameter and replace occurances of t with (type 'a). So your code might be written as

let create<'a> (mgr: PluginManager) =
  { for x in assemblies mgr
    for y in HA.types x
    when Helper.is_a (type 'a) y
    -> (HA.domain x).CreateInstanceAndUnwrap((HA.assembly x).FullName, y.FullName) :?> 'a}

See also [link:cs.hubfs.net] for a similar problem.
By on 12/21/2007 11:33 PM ()
Hi,

You are correct in that 'a and t refer to the same statically known type (which is an abstract class/interface).

I am actually the person who had started that last thread you reference as well :). Unluckily, the little gem (type 'a) didn't make it into the last thread, and I have just returned to working on that library after a long break.

Thank you very much for the answer, as I will be putting it to use immediately. I'm getting on quite well with F#, but there are still certain areas such as types (obviously), events and so on that confuse me with regards to how F# and the rest of .net interact.

Thanks again,

z.
By on 12/22/2007 12:22 AM ()

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