How to consume BlockingCollection<'a>.TryTake in F#

问题

How do I go about using the TryTake method on a BlockingCollection<'a> passing in a timeout period in milliseconds?

Heres the signature:

BlockingCollection.TryTake(item: byref, millisecondsTimeout: int) : bool

is it possible to use the Tuple method of avoiding passing a ref type like on the Dictionary.TryGet methods?

i.e.
let success, item = myDictionary.TryGetValue(client)

Im struggling with this particular signature, any suggestions would be great.

Cheers!

回答1:

I believe that you can only use that technique for byref parameters which occur at the end of the parameter list (this is similar to the rule for optional parameters). So if BlockingCollection.TryTake were defined with signature int * 'T byref -> bool it would work, but since it's defined as 'T byref * int -> bool it won't.

For example:

open System.Runtime.InteropServices

type T =
  static member Meth1(a:int, [<Out>]b:string byref, [<Out>]c:bool byref) : char = 
    b <- sprintf "%i" a
    c <- a % 2 = 0
    char a
  static member Meth2([<Out>]b:string byref, [<Out>]c:bool byref, a:int) : char = 
    b <- sprintf "%i" a
    c <- a % 2 = 0
    char a

//  ok
let (r,b,c) = T.Meth1(5)
//  ok
let (r,c) = T.Meth1(5,ref "test")
// ok
let r = T.Meth1(5, ref "test", ref true)
// doesn't compile
let (r,b,c) = T.Meth2(5)
// doesn't compile
let (r,c) = T.Meth2(ref "test", 5)
// ok
let r = T.Meth2(ref "test", ref true, 5)

来源：https://stackoverflow.com/questions/4927649/how-to-consume-blockingcollectiona-trytake-in-f