如何实现与Dictionary.TryGetValue相同的行为

TryGetValue 有一个out参数,所以您需要在F#中执行相同的操作(通过 byref OutAttribute ):

open System.Runtime.InteropServices 
type MyDict<'K,'V when 'K : equality>() =  // '
    let d = new System.Collections.Generic.Dictionary<'K,'V>()
    member this.TryGetValue(k : 'K, [<Out>] v: byref<'V>) =
        let ok, r = d.TryGetValue(k)
        if ok then
            v <- r
        ok            

let d = new MyDict<string,int>()
let ok, i = d.TryGetValue("hi")
let mutable j = 0
let ok2 = d.TryGetValue("hi", &j)

就我个人而言,我从来都不喜欢 bool TryXXX(stringToParseOrKeyToLookup, out parsedInputOrLookupValue_DefaultIfParseFailsOrLookupNotFound) Some / None 图案会很完美(比如 Seq.tryFind

type MyClass () =
  let items = System.Collections.Generic.Dictionary<string,int>()
  do 
    items.Add ("one",1)
    items.Add ("two",2)
    items.Add ("three",3)
  member this.TryGetValue (key) =
    match items.TryGetValue(key) with
        | (true, v) -> Some(v)
        | _ -> None

let c = MyClass()

let printKeyValue key =
    match c.TryGetValue(key) with
    | Some(value) -> printfn "key=%s, value=%i" key value
    | None -> printfn "key=%s, value=None" key

//> printKeyValue "three";;
//key=three, value=3
//val it : unit = ()
//> printKeyValue "four";;
//key=four, value=None
//val it : unit = ()