F#错误编译 [英] F# Error compiling

问题描述

我有以下导致编译错误的F#代码:

I have the following F# Code that is causing a compile error:

persistence.fs(32,21):错误FS0072:基于此程序点之前的信息，对不确定类型的对象进行查找.在此程序指向之前可能需要类型注释，以约束对象的类型.这样可以解决查找问题.

persistence.fs(32,21): error FS0072: Lookup on object of indeterminate type based on information prior to this program point. A type annotation may be needed prior to this program point to constrain the type of the object. This may allow the lookup to be resolved.

错误在"serializer.write ..."行.

The error is at the line "serializer.write...."

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)

推荐答案

尽管可以调用serializer.write(elem, writer_)之类的write函数，这很好，但是不能.您必须改为这样调用它:

Although it'd be nice if you could invoke the write function like serializer.write(elem, writer_), you can't. You have to invoke it like this instead:

(^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)

注意:可以编译，但是我不知道它是否可以完成您想要的操作.

Caveat: this compiles, but I have no idea if it does what you want it to do.

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