How to get the child declaring type from an expression?

Question

I have a Parent / Child class hierarchy where the Parent abstractly declares a string property and the Child class implements it: ``` abstract class Parent { public abstract string Value { get; } } class Child : Parent { public override string Value { get { return null; } } } ``` When I use an expression that explicitly (or implicitly) uses the Child class, I expect the Expressions's MemberInfo's DeclaringType to be 'Child', but instead it is Parent: ``` Child child = new Child(); Expression> expression = (() => child.Value); MemberInfo memberInfo = expression.GetMemberInfo(); Assert.AreEqual(typeof(Child), memberInfo.DeclaringType); // FAILS! ``` The assertion fails because the DeclaringType is Parent. Is there something I can do in declaring my expression or consuming it to reveal the actual use of the Child type? NOTE: GetMemberInfo() above as an extension method (I even forgot we had written this!): ``` public static class TypeExtensions { ///

/// Gets the m…

Accepted Answer

No - this is an accurate representation of what gets emitted by the C# compiler. The override is effectively ignored when looking for the member - the compiler only cares about the type that originally declared the member. You can see this for yourself by compiling code and then looking at the IL. This method:

```
static void Main()
{
    Child c = new Child();
    string x = c.Value;
}
```

is compiled into this IL:

```
IL_0000:  nop
IL_0001:  newobj     instance void Child::.ctor()
IL_0006:  stloc.0
IL_0007:  ldloc.0
IL_0008:  callvirt   instance string Parent::get_Value()
IL_000d:  stloc.1
IL_000e:  ret
```

One point of trivia: the VB compiler doesn't work the same way, so this method:

```
Public Shared Sub Main(Args As String())
    Dim x As Child = New Child()
    Dim y As String = x.Value
End Sub
```

is compiled as:

```
IL_0000:  newobj     instance void [lib]Child::.ctor()
IL_0005:  stloc.0
IL_0006:  ldloc.0
IL_0007:  callvirt   instance string [lib]Child::get_Value()
IL_000c:  stloc.1
IL_000d:  ret
```

How to get the child declaring type from an expression?

Solution

Problem