F# 编译错误

我有以下导致编译错误的 F# 代码：

persistence.fs(32,21)：错误 FS0072：根据此程序点之前的信息查找不确定类型的对象。在此程序点之前可能需要类型注释来约束对象的类型。这可以使查找得以解决。

错误出现在“serializer.write....”行

任何帮助，将不胜感激。

namespace persisitence
open System.Collections.Generic
open System
open System.IO

type LocalData<'T> =
    struct
        val mutable elements_ : 'T list
        val mutable lock_ : obj
        new(e: 'T list) = { elements_ = e ; lock_ = new obj() }
    end

type BinaryPersistenceOut<'T, ^W when ^W: (member write : ('T * BinaryWriter) -> unit)>(fn: string, serializer: ^W) as this = 
    let writer_ = new BinaryWriter(File.Open(fn, FileMode.Append))
    let mutable localdata_ = new LocalData<'T>([])
    let serializer_ = serializer
    let NUM_SECS_IN_MIN = 60
    let NUM_MSECS_IN_SEC = 1000
    let NUM_MIN_BETWEEN_COMMITS = 2
    let TIME_TO_WAIT = 15
    let closed_ = false

    let freq_ = NUM_MIN_BETWEEN_COMMITS * NUM_SECS_IN_MIN * NUM_MSECS_IN_SEC
    let path_ = fn
    let timer_ = new System.Timers.Timer((float) (NUM_MIN_BETWEEN_COMMITS * NUM_MSECS_IN_SEC) )

    let writetofile = 
        fun (arg: Timers.ElapsedEventArgs ) ->
            lock localdata_.lock_ ( fun () -> 
             if closed_ = false then
                for elem in localdata_.elements_ do
                    serializer.write(elem, writer_)
             )  

    do 
        timer_.Elapsed.Add(writetofile)

虽然如果你能调用的话那就太好了write功能类似于serializer.write(elem, writer_)，你不能。你必须像这样调用它：

(^W: (member write : ('T * BinaryWriter) -> unit) (serializer, (elem, writer_)))

完整代码块：

type BinaryPersistenceOut<'T, ^W when ^W: (member write : ('T * BinaryWriter) -> unit)> (fn: string, serializer: ^W) as this = 
    let writer_ = new BinaryWriter(File.Open(fn, FileMode.Append))
    let mutable localdata_ = new LocalData<'T>([])
    let serializer_ = serializer
    let NUM_SECS_IN_MIN = 60
    let NUM_MSECS_IN_SEC = 1000
    let NUM_MIN_BETWEEN_COMMITS = 2
    let TIME_TO_WAIT = 15
    let closed_ = false

    let freq_ = NUM_MIN_BETWEEN_COMMITS * NUM_SECS_IN_MIN * NUM_MSECS_IN_SEC
    let path_ = fn
    let timer_ = new System.Timers.Timer((float) (NUM_MIN_BETWEEN_COMMITS * NUM_MSECS_IN_SEC) )

    let writetofile = 
        fun (arg: Timers.ElapsedEventArgs ) ->
            lock localdata_.lock_ ( fun () -> 
             if closed_ = false then
                for elem in localdata_.elements_ do
                    (^W: (member write : ('T * BinaryWriter) -> unit) (serializer, (elem, writer_)))
             )  

    do 
        timer_.Elapsed.Add(writetofile)

警告：这可以编译，但我不知道它是否符合您的要求。