[英]pass expressions and lambdas parameter to C# extension method in F#
我正在努力解決這個問題,因為我只是F#的初學者,目前我正在學習F#,通過在F#中為C#代碼創建單元測試,如F#所示,以獲得樂趣和利潤。
問題。
我有以下C#類
public class ObjectMapper<TSource, TTarget>
where TTarget : class, new() {
public readonly TSource Source;
public readonly TTarget Target;
public ObjectMapper(TSource source) {
this.Source = source;
this.Target = new TTarget();
}
public ObjectMapper<TSource, TTarget> Populate<T>(
Expression<Func<TTarget, T>> targetAccessor,
Func<TSource, T> sourceValue) {
var targetPropertyInfo = targetAccessor.ToPropertyInfo();
targetPropertyInfo.SetValue(this.Target, sourceValue(this.Source));
return this;
}
}
我開始嘗試在F#中編寫一個簡單的單元測試
module CompanyName.Utils.Test.ObjectMapper
open System
open Xunit
open Swensen.Unquote
open Microsoft.FSharp.Linq.RuntimeHelpers // do I need this?
open CompanyName.Utils // the namespace of the C# class above
type Source(name: string, code: int, date: DateTime) =
member thi.Name = name
member this.Code = code
member this.Date = date
type Target() =
member this.Id: string = System.String.Empty
member this.Name: string = System.String.Empty
member this.Code: int = 0
member this.Date: DateTime = System.DateTime.MinValue
[<Fact>]
let ``ObjectMapper.Populate maps property values from source to target``() =
// arrange
let name = @"name"
let code = 123
let date = new System.DateTime(1980,2,15)
let source = Source(name, code, date)
// let target = Target()
let mapper = ObjectMapper<Source, Target>(source)
// act // this is how I would like it to be!
mapper.Populate(t => t.Name, s => s.Name)
mapper.Populate(t => t.Code, s => s.Code)
mapper.Populate(t => t.Date, s => s.Date)
mapper.Populate(t => t.Id, s => s.Date+s.Code+s.Name)
// assert
test<@ mapper.Target.Name = source.Name @>
Assert.Equal(mapper.Target.Name, source.Name)
test<@ mapper.Target.Code = source.Code @>
Assert.Equal(mapper.Target.Code, source.Code)
test<@ mapper.Target.Date = source.Date @>
Assert.Equal(mapper.Target.Date, source.Date)
test<@ mapper.Target.Id = @"1980-2-15123name" @>
Assert.Equal(mapper.Target.Id, @"1980-2-15123name")
Assert.True(false)
我的問題在於測試的斷言部分,理想情況下,我希望能夠像上面代碼中使用的那樣傳遞lambda。 不幸的是,這根本不起作用,我試圖引用其他關於堆棧溢出的帖子,其中討論了這個和相關的主題。 總的來說,這些帖子的級別對我來說有點太高了,雖然我理解了一般概念但是我沒有真正掌握必要的細節來將上面的元代碼轉換為在F#中有意義的東西,最重要的是編譯和運行。
如果你能幫助我,我將非常感激
請隨意對我認為適合幫助我成為F#以及C#中更好的開發人員的代碼發表任何評論,我根本不介意。 我知道上面的代碼非常簡單,有些部分冗余且效率低下。 我認為要保持基本,以免影響核心問題。
對於那些可能熟悉一種風格但不熟悉另一種風格的人,可以在Unquote和MSTest樣式中重復這些斷言。
非常感謝你的幫助。
下面是Fyodor Soiki解釋的工作代碼
module CompanyName.FSharp.UtilsFunctions
// Efficient concatenation of objects into a string with string builder
// https://stackoverflow.com/questions/18595597/is-using-a-stringbuilder-a-
right-thing-to-do-in-f
let strconc =
fun (data) ->
let sb = new System.Text.StringBuilder()
for o in data do sb.Append(o.ToString()) |> ignore
sb.ToString()
// examples
strconc ["one"; "two"] |> printfn "%s"
strconc [1;2;3] |> printfn "%s"
strconc (["one"; "two"; 3 ]: list<obj>) |> printfn "%s"
module LogXtreme.Utils.Test.ObjectMapper
open System
open Xunit
open Swensen.Unquote
open CompanyName.Utils
open CompanyName.FSharp.UtilsFunctions
type Source(name: string, code: int, date: DateTime) =
member thi.Name = name
member this.Code = code
member this.Date = date
type Target() =
member val Id: string = System.String.Empty with get, set
member val Name: string = System.String.Empty with get, set
member val Code: int = 0 with get, set
member val Date: DateTime = System.DateTime.MinValue with get, set
[<Fact>]
let ``ObjectMapper.Populate maps property values from source to target``() =
// arrange
let name = @"name"
let code = 123
let date = new System.DateTime(1980,2,15)
let source = Source(name, code, date)
let mapper = ObjectMapper<Source, Target>(source)
let expectedId = strconc ([source.Name; source.Code; source.Date]: list<obj>)
// act
mapper.Populate((fun t -> t.Name), fun s -> s.Name) |> ignore
mapper.Populate((fun t -> t.Code), fun s -> s.Code) |> ignore
mapper.Populate((fun t -> t.Date), fun s -> s.Date) |> ignore
mapper.Populate((fun t -> t.Id), fun s -> strconc ([s.Name; s.Code; s.Date]: list<obj>)) |> ignore
// assert
test<@ mapper.Target.Name = source.Name @>
test<@ mapper.Target.Code = source.Code @>
test<@ mapper.Target.Date = source.Date @>
test<@ mapper.Target.Id = expectedId @>
測試現在通過。
一般來說,F#往往會避免神奇的轉換,因為它們通常會導致細微的,難以發現的錯誤。 但是,在一些特殊情況下,主要是為了支持C#互操作場景,它會妥協。
特別是,當調用期望Expression<_>
的對象方法時,編譯器會將F#lambda表達式轉換為C#引用(與C#編譯器的方式相同)。 這意味着你可以將普通的F#lambdas傳遞給你的方法:
mapper.Populate( (fun t -> t.Name), fun s -> s.Name )
第一個lambda周圍的括號是必要的。 沒有它們,整個事物被解釋為fun t -> ( t.Name, fun s -> s.Name )
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