F# - How to populate an System.Collections.Generic.List from array

I have following code that populates a System.Collections.Generic.List I don't like it so I was wondering if there is a better way to do this.

let getDirectories = 
        Directory.GetDirectories(_baseFolder)
let languagesList = new System.Collections.Generic.List<string>()
Seq.cast getDirectories 
|> Seq.map(fun dir -> (new DirectoryInfo(dir)).Name) 
|> fun range -> languagesList.AddRange(range)

From stackoverflow

• Have you tried:

  let list = new System.Collections.Generic.List<string>(arr)
  

  List<'T> has a constructor that takes an IEnumerable<'T> so it happily takes any seq<'T> you pass to it.

  : +1 he he (embaracced) ok now I shall punish myself.

• In addition to Mehrdad's answer

  I find it helpful to define helper modules for many standard collections and .Net types to make them more F# friendly. Here I would define the following

  module BclListUtil =
    let ofArray (arr: 'T array) = new System.Collections.Generic.List<'T>(arr)
    let ofSeq (arr: 'T seq) = new System.Collections.Generic.List<'T>(arr)
  

  Then you could change your original code to the following

  let getDirectories = 
          Directory.GetDirectories(_baseFolder)
  let languagesList = 
        getDirectiories
        |> Seq.map (fun dir -> (new DirectoryInfo(dir)).Name)
        |> BclListUtil.ofSeq
  

  kvb : Note also that you can use the shorter (and potentially less ambiguous) type abbreviation `ResizeArray<_>` instead of `System.Collections.Generic.List<_>`.

  JaredPar : @kvb, thanks, I didn't realize there was already a type alias present.

• The F# alias for System.Collections.Generic.List<_> is ResizeArray<_> as kvb noted. The F# PowerPack includes a ResizeArray module for working with BCL Lists in an idiomatic F# fashion similar to the Seq and List modules.

  However, for some strange reason this module seems to include ofArray and ofList and toSeq but not ofSeq.