{"id":509,"date":"2008-10-12T14:08:00","date_gmt":"2008-10-12T12:08:00","guid":{"rendered":"http:\/\/www.navision-blog.de\/2008\/10\/12\/f-option-types-in-c-verwenden\/"},"modified":"2008-10-12T14:28:19","modified_gmt":"2008-10-12T12:28:19","slug":"f-option-types-und-generische-listen-in-c-verwenden","status":"publish","type":"post","link":"http:\/\/www.navision-blog.de\/blog\/2008\/10\/12\/f-option-types-und-generische-listen-in-c-verwenden\/","title":{"rendered":"F# option types und generische Listen in C# verwenden"},"content":{"rendered":"

Luis Fallas<\/a> beschreibt in seinem Blog (\u201cExploring Beautiful Languages\u201d) an einem sehr schönen Beispiel, wie man die F# option types mit Hilfe von Extension Methods in C# verwenden<\/a> kann.<\/p>\n

Hier ist eine generische Variante zu seiner Exists()-Methode:<\/p>\n

open<\/span> System.Runtime.CompilerServices <\/p>\n

\n
[<Extension>]<\/pre>\n
module<\/span> Extensions =<\/pre>\n
  [<Extension>]<\/pre>\n
  let<\/span> Exists(opt : 'a option) =<\/pre>\n
    match<\/span> opt with<\/span><\/pre>\n
      | Some _ -><\/span> true<\/span><\/pre>\n
      | None \u2013><\/span> false<\/span><\/pre>\n<\/div>\n
Auf ähnlichem Wege kann man übrigens auch die generischen F#-Listen<\/a> in System.Collections.Generic.List<T> umwandeln:<\/p>\n
\n
[<Extension>]    <\/pre>\n
let<\/span> ToCSharpList(list : 'a list) =<\/pre>\n
  let<\/span> csharpList = <\/pre>\n
    new<\/span> System.Collections.Generic.List<'a>()<\/pre>\n
  list |> List.iter (fun<\/span> item -><\/span> csharpList.Add item)<\/pre>\n
  csharpList<\/pre>\n<\/div>\n
Der umgekehrte Weg (von C# nach F#) ist fast analog, allerdings muss man die Liste drehen:<\/p>\n
\n
static<\/span> class<\/span> Extensions<\/span><\/pre>\n
{<\/pre>\n
\n
  \/\/\/<\/span> <\/span><summary><\/span><\/pre>\n
  \/\/\/<\/span> Converts a System.Collections.Generic.List<\/span><T><\/span> <\/span><\/pre>\n
  \/\/\/<\/span> <\/span>in the corresponding F# list.<\/span><\/pre>\n
  \/\/\/<\/span> <\/span><\/summary><\/span><\/pre>\n
  <\/span>public<\/span> static<\/span> Microsoft.FSharp.Collections.List<\/span><T> <\/pre>\n<\/p><\/div>\n
     ToFSharpList<T>(this<\/span> List<\/span><T> list)<\/pre>\n
  {<\/pre>\n
      var<\/span> fSharpList = <\/pre>\n
        Microsoft.FSharp.Collections.List<\/span><T>.Empty;<\/pre>\n
      for<\/span> (int<\/span> i = list.Count - 1; i >= 0; i--)<\/pre>\n
       fSharpList = <\/pre>\n
          Microsoft.FSharp.Collections.List<\/span><T>.Cons(<\/pre>\n
            list[i], <\/pre>\n
            fSharpList);<\/pre>\n
      return<\/span> fSharpList;<\/pre>\n
  }<\/pre>\n
}<\/pre>\n<\/div>\n","protected":false},"excerpt":{"rendered":"
Luis Fallas beschreibt in seinem Blog (\u201cExploring Beautiful Languages\u201d) an einem sehr schönen Beispiel, wie man die F# option types mit Hilfe von Extension Methods in C# verwenden kann. Hier ist eine generische Variante zu seiner Exists()-Methode: open System.Runtime.CompilerServices [<Extension>] module Extensions =   [<Extension>]   let Exists(opt : ‘a option) =     match opt […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[12,448],"tags":[81,456,455,664,454,452,453],"_links":{"self":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/509"}],"collection":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/comments?post=509"}],"version-history":[{"count":9,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/509\/revisions"}],"predecessor-version":[{"id":521,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/posts\/509\/revisions\/521"}],"wp:attachment":[{"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/media?parent=509"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/categories?post=509"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.navision-blog.de\/blog\/wp-json\/wp\/v2\/tags?post=509"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}