Microbenchmark for https://github.com/Microsoft/visualfsharp/pull/2138

program.fs

open System
open System.IO

let illegalPathChars =
    let chars = Path.GetInvalidPathChars ()
    chars

let checkPathForIllegalChars (path:string) =
    let len = path.Length
    for i = 0 to len - 1 do
        let c = path.[i]
        
        // Determine if this character is disallowed within a path by
        // attempting to find it in the array of illegal path characters.
        for badChar in illegalPathChars do
            if c = badChar then
                failwith "apa"

let time f message =
        let t = System.Diagnostics.Stopwatch.StartNew()
        try f () finally
        printf "%s took %dms\n" message t.ElapsedMilliseconds

let times n f message = 
   time (fun () -> 
          for i in 1 .. n do
           f ()) message

let illegalPathChars2 =
    Path.GetInvalidPathChars () |> set

let checkPathForIllegalChars2 (path:string) =
    let len = path.Length
    for i = 0 to len - 1 do
        let c = path.[i]
        // Determine if this character is disallowed within a path by
        // attempting to find it in the array of illegal path characters.
        if illegalPathChars2.Contains c then
                failwith "apa"

let checkPathForIllegalChars3  =
    let chars = new System.Collections.Generic.HashSet<_>(Path.GetInvalidPathChars())
    (fun (path:string) -> 
      let len = path.Length
      for i = 0 to len - 1 do
          let c = path.[i]
          if chars.Contains c then
                  failwith "apa")



let checkPathForIllegalChars4  =
    let invalidChars = new System.Collections.Generic.HashSet<_>(Path.GetInvalidPathChars())
    (fun (path:string) -> 
      let chars = new System.Collections.Generic.HashSet<_>(path)
      let intersection = chars.IntersectWith(invalidChars)
      if chars.Count > 0 then
                  failwith "apa")

let checkPathForIllegalChars5  =
    let chars = new System.Collections.Generic.HashSet<_>(Path.GetInvalidPathChars())
    (fun (path:string) -> 
      let len = path.Length
      for i = 0 to path.Length - 1 do
          let c = path.[i]
          if chars.Contains c then
                  failwith "apa")

let checkPathForIllegalChars6  =
    let chars = new System.Collections.Generic.HashSet<_>(Path.GetInvalidPathChars())
    (fun (path:string) -> 
      for c in path do
          if chars.Contains c then
                  failwith "apa")


let checkPathForIllegalChars7  =
    let chars = new System.Collections.Generic.HashSet<_>(Path.GetInvalidPathChars())
    (fun (path:string) -> 
          if chars.Overlaps path then
                  failwith "apa")

let checkPathForIllegalChars8 (path:string) =
    for c in path do
        for badChar in illegalPathChars do
            if c = badChar then
                failwith "apa"

[<EntryPoint>]
let main argv = 

    times 100000 (fun () -> checkPathForIllegalChars "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "fsharp"
    times 100000 (fun () -> checkPathForIllegalChars2 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "FsharpSet"
    times 100000 (fun () -> checkPathForIllegalChars3 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSet"
    times 100000 (fun () -> checkPathForIllegalChars4 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "Intersect"
    times 100000 (fun () -> checkPathForIllegalChars5 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetBounds"
    times 100000 (fun () -> checkPathForIllegalChars6 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetForIn"
    times 100000 (fun () -> checkPathForIllegalChars7 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetOverlaps"
    times 100000 (fun () -> checkPathForIllegalChars8 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "fsharpForIn"

    times 100000 (fun () -> checkPathForIllegalChars "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "fsharp"
    times 100000 (fun () -> checkPathForIllegalChars2 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "FsharpSet"
    times 100000 (fun () -> checkPathForIllegalChars3 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSet"
    times 100000 (fun () -> checkPathForIllegalChars4 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "Intersect"
    times 100000 (fun () -> checkPathForIllegalChars5 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetBounds"
    times 100000 (fun () -> checkPathForIllegalChars6 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetForIn"
    times 100000 (fun () -> checkPathForIllegalChars7 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "HashSetOverlaps"
    times 100000 (fun () -> checkPathForIllegalChars8 "c:\\dev\\myproject\\utilities\\longstring with spaces\\filename.fs") "fsharpForIn"


    printfn "%A" argv
    0 // return an integer exit code