如何将项目类型转换为共享类库类型

Question

(C# code samples are at the bottom of the question.)

I have a class library shared between a number of solutions, with a type called SharedType . I have a method in the class library which processes a collection of this type:

Sub ProcessSharedTypeEnumerable(src As IEnumerable(Of SharedType))
    'do something here
End Sub

Each solution has its own specific type that should map/convert to the SharedType :

Namespace Project1
    Class ProjectType
    End Class
End Namespace

How can I call ProcessSharedTypeEnumerable without having to convert ProjectType to SharedType at the call site?

Dim lst As New List(Of ProjectType)
'populate list

'instead of this:
ProcessSharedTypeEnumerable(lst.Select(Function(x) New SharedType With { 'populate members here' })
'use this:
ProcessSharedTypeEnumerable(lst)

---

I know I can have the project type implement an interface from the class library, which has a method that maps to the shared type

Public Interface ISharedTypeMappable
    Function ToSharedType() As SharedType
End Interface

Then the ProcessSharedTypeEnumerable method can take IEnumerable(Of ISharedTypeMappable) and I can call .Select(Function(x) x.ToSharedType) within ProcessSharedTypeEnumerable to get IEnumerable(Of SharedType) .

---

Is there a "more correct" way to do this? Generic covariance and implicit conversion? Some .NET built-in conversion mechanism?

---

C# code samples

Class library method:

static class Utils { //I know it's an awful name ...
    static void ProcessSharedTypeEnumerable(IEnumerable<SharedType> src) {
        //do something here
    }
}

Project code:

var lst = new List<ProjectType>();
//populate list

//instead of this:
Utils.ProcessSharedTypeEnumerable(lst.Select(x=>new SharedType { /* populate properties here */}));
//do this
Utils.ProcessSharedTypeEnumerable(lst);

---

Update

I don't want to have ProjectType inherit from SharedType for two reasons (1) ProjectType already inherits from a different base type, and (2) SharedType may have members that should not be on ProjectType .

Answer 1

Inheritance?

Sub Main()
    Dim lst As New List(Of ProjectType) From {
        New ProjectType With {.s = "1"},
        New ProjectType With {.s = "2"},
        New ProjectType With {.s = "3"}
    }
    SharedType.ProcessSharedTypeEnumerable(lst)
End Sub

Shared Sub ProcessSharedTypeEnumerable(src As IEnumerable(Of SharedType))
    For Each st As SharedType In src
        MsgBox(st.s)
    Next
End Sub

Class SharedType
    Property s As String
End Class

Class ProjectType
    Inherits SharedType
End Class

Answer 2

EDIT: This is now a community wiki answer

As requested, here's my attempt at implementing Operator Widening CType . It does not work, though. Maybe someone reading this can work it out.

Module Module1

  Sub Main()
    Dim lst As New List(Of ProjectType) From {
        New ProjectType With {.t = "1"},
        New ProjectType With {.t = "2"},
        New ProjectType With {.t = "3"}
    }
    MsgBox(CType(lst(0), SharedType).s) 'This works'
    ProcessSharedTypeEnumerable(lst) 'This does not :-( '
    ProcessSharedTypeEnumerable(lst.Cast(Of SharedType).ToList) 'Neither does this :-( '
  End Sub

  Sub ProcessSharedTypeEnumerable(src As IEnumerable(Of SharedType))
    For Each st As SharedType In src
      MsgBox(st.s)
    Next st
  End Sub

  Class SharedType
    Property s As String
  End Class

  Class ProjectType
    Property t As String

    Public Shared Widening Operator CType(p As ProjectType) As SharedType
      Return New SharedType With {.s = p.t}
    End Operator
  End Class
End Module