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f#type-extension

F# extend jagged array type

I have read the question F# how to extended the generic array type? and it's answer, and it's pretty close to what I wan't to do. Is it possible to extend the type 'T[][], just like it is with 'T[]?

Solution

  • The jagged array [][] is an array[] specialized in another array.

    You can use [,] which is a 2D array:

    type 'T ``[,]`` with
    member a.First = a.GetValue(0,0)

(array2D [| [| 1 .. 10 |] ; [| 11 .. 20 |] |] ).First

    But if you really want to use [][] you can't do it with this F# specific notation, it is not possible to declare it specialized since this notation mirrors the Type Definition, so you have to do it the .NET way:

    [<System.Runtime.CompilerServices.Extension>]
module Extensions =

    [<System.Runtime.CompilerServices.Extension>]   
    let First   (x  :_ [][]) = x.[0].[0]

    It will work when accessed from C#, but from F# I think you will need F# 3.1