在f#中声明一个泛型函数

Question

我试图在F#中编写我的第一个泛型函数,看起来我在这里缺少一些概念:

module Assert =
    let ThrowsException<'e : exn>  functionUnderTest  =
    try 
        let result = functionUnderTest
        printfn "fails"
    with 
    | :? 'e  ->  printfn  "succeeds"
    | _  -> printfn "fails"

stdin(18,28):错误FS0010:模式中出现意外符号':'.预期的">"或其他令牌.

我希望能够使用我的函数来测试是否引发了异常.

let myFunction=HttpClient.postDocRaw "http://notexisting.com/post.php" "hello=data"
Assert.ThrowsException System.Net.WebException myFunction

我想实现这个测试工具,所以如果有人有解决方案,这很好,但此外,我正在学习F#,我想知道在哪里出错我试图编写这样的函数.

最终代码:

module Assert =
    let ThrowsException<'e when 'e :> exn>  functionUnderTest  =
        try 
           let actual = functionUnderTest()
           printfn "succeeds"
        with 
        | :? 'e  ->  printfn  "succeeds"
        | _  ->  Assert.Fail()


[<TestClass>]
type HttpClientTest() = 
[<TestMethod>]
    member x.PostDataWrongUrl() = 
        Assert.ThrowsException<System.Net.WebException>  (fun() ->  HttpClient.postDocRaw "http://notexisting.com/post.php" "hello=data")

Answer 1

错误显示"Expected'>'"因为类型约束采用了表单'T when 'T :> baseType.你的代码应该是:

module Assert =
  let ThrowsException<'e when 'e :> exn> functionUnderTest =
    try 
      let result = functionUnderTest
      printfn "fails"
    with 
      | :? 'e -> printfn  "succeeds"
      | _  -> printfn "fails"

有关详细信息,请参阅MSDN上的约束.