Item上的静态约束

Question

我试图写一个选项价值版本的＆＃34; TryGetValue＆＃34;这将适用于任何实现IDictionary或IReadOnlyDictionary的对象。我有这个：

let inline contains   (key:^key) (dictionary:^dic )=
    (^dic: (member ContainsKey: ^key -> bool) (dictionary, key) ) 

let inline tryGetValue (dictionary:^dic )  (key:^key)=
    if contains key dictionary then  
        let value = ( ^dic : (member  get_Item: ^key -> ^value )  (dictionary, key) )   (dictionary) ) key
        value |> Some
    else None  

＆＃34;值＆＃34;的定义生成一个警告，表示名称为get_Item的成员约束具有特殊状态，这可能导致运行时错误。我该怎么办？

Answer 1

如何使用TryGetValue代替ContainsKey和Item？

let inline tryGetValue dic key =
    let mutable value = Unchecked.defaultof< ^value>
    let contains = (^dic : (member TryGetValue : ^key * byref< ^value> -> bool) (dic, key, &value))
    if contains then Some value else None