Pass and lambdas parameter for C # extension method in F #

Question

I struggle with this because I'm just a beginner in F #, and I'm currently involved in the F # learning process by creating unit tests for C # code in F #, as suggested in F # for fun and for profit.

Problem.

I have the following C # class

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;
    }
}

and I started by trying to write a simple unit test in F #

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)

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.

Fyodor Soiki

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 @>

.

Answer 1

, F # , , . , #, .

, , Expression<_>, F # # ( , #). , F # lambdas :

mapper.Populate( (fun t -> t.Name), fun s -> s.Name )

. fun t -> ( t.Name, fun s -> s.Name )