[英]F# Generic Problem: could not be generalized because it would escape its scope
I have this defined in a common place: 我在一个普通的地方定义了这个:
[<DataContract>]
type ResultObject = {
[<DataMember>]
mutable field1: string
[<DataMember>]
mutable field2: string
[<DataMember>]
mutable field3: int
}
let createCache<'T> () =
Dictionary<_, 'T option>(HashIdentity.Structural)
let memoizeSingleParamWithCallback<'R, 'P when 'P : equality> functionToMemoize =
let cache = createCache<'R>()
// return a function that takes two parameters a parameter to the functionToMemoize and a callback
fun (parameter: 'P) (callback: Action<_>) ->
// form a unique cache key the parameterValue
let key = parameter
// check to see if the cache contains they key
match cache.ContainsKey(key) with
// if so invoke the callback with the cache value (need to conver to Some)
| true -> callback.Invoke(cache.[key])
// if not, invoke the RPC function, store the value, and perform the callback
| false ->
// create an internim callback to intercept the RPC function results,
// store the value, and perform the final callback
let updateCache (results: 'R option) =
match results with
// no results returned - invoke call back with None none
| None ->
cache.[key] <- None
callback.Invoke(None)
// results returned - store them and invoke the call back
| Some result ->
cache.[key] <- Some(result)
callback.Invoke(Some(result))
functionToMemoize parameter <| new Action<_>(updateCache)
And am attempting to use it as so: 并尝试按以下方式使用它:
let findTickers (partialTicker : String) (callbackUI : Action<_>) =
let lstOfResultObjects = [{field1=""; field2=""; field3=3}]
callbackUI.Invoke(Some(lstOfResultObjects))
let findTickersMemoize = memoizeSingleParamWithCallback<ResultObject array, string> findTickers
and recieve this error on the memoize function definition: 并在备忘录功能定义中收到此错误:
This code is not sufficiently generic. 该代码不够通用。 The type variable 'P when 'P : equality could not be generalized because it would escape its scope. 类型变量'P when'P:equal不能被概括,因为它将逃避其范围。
My two questions are: 我的两个问题是:
Everythign compiles by removing by typing parameter to string: Everythign通过在字符串中键入参数来删除来进行编译:
fun (parameter: 'P) (callback: Action<_>) ->
()
HOWEVER I want to be able to memoize, more than functions with a: String Action<_> signature, ideally the string could be an int, float, object - whatever... 但是,除了具有以下功能的函数外,我还希望能够记住:String Action <_>签名,理想情况下,该字符串可以是int,float,object-等等。
The issue is that you have provided a single type parameter 'T
on your definition of createCache
, but when you instantiate it in memoizeSingleParamWithCallback
, you want to get back a Dictionary<'P, 'R option>
. 问题是您在createCache
的定义上提供了一个类型参数'T
,但是当在memoizeSingleParamWithCallback
实例化它时,您想要获取Dictionary<'P, 'R option>
。 You can actually just remove some of the type parameters and annotations to get your code to work: 实际上,您可以删除一些类型参数和注释以使代码正常工作:
let createCache() =
Dictionary<_, _>(HashIdentity.Structural)
let memoizeSingleParamWithCallback functionToMemoize =
let cache = createCache()
// return a function that takes two parameters a parameter to the functionToMemoize and a callback
fun (parameter: 'P) (callback: Action<_>) ->
// form a unique cache key the parameterValue
let key = parameter
// check to see if the cache contains they key
match cache.ContainsKey(key) with
// if so invoke the callback with the cache value (need to conver to Some)
| true -> callback.Invoke(cache.[key])
// if not, invoke the RPC function, store the value, and perform the callback
| false ->
// create an internim callback to intercept the RPC function results,
// store the value, and perform the final callback
let updateCache (results: 'R option) =
match results with
// no results returned - invoke call back with None none
| None ->
cache.[key] <- None
callback.Invoke(None)
// results returned - store them and invoke the call back
| Some result ->
cache.[key] <- Some(result)
callback.Invoke(Some(result))
functionToMemoize parameter <| new Action<_>(updateCache)
Now F# infers the most general types that are applicable, which results in createCache
correctly depending on two implicit type parameters. 现在,F#推断适用的最通用类型,这取决于两个隐式类型参数正确地创建了createCache
。
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