How is Reflection implemented in C#?

Question

I got curious as to where Type.GetType() is implemented, so I took a peek at the assembly and noticed Type.GetType() calls base.GetType() and since Type inherits from MemberInfo I took a look and it is defined as _MemberInfo.GetType() which returns this.GetType(). Since I cannot find the actual code that shows how C# can get type information I would like to know:

How does the CLR get Type and MemberInfo from objects at Runtime?

Answer 1

The ACTUAL source for .NET Framework 2.0 is available on the internet (for educational purposes) here: http://www.microsoft.com/en-us/download/details.aspx?id=4917

This is the C# Language implementation. You can use 7zip to unpack it. You will find the reflection namespace here (relatively):

.\sscli20\clr\src\bcl\system\reflection

I am digging for the specific implementation you are asking about, but this is a good start.

UPDATE: Sorry, but I think its a dead end. Type.GetType() calls to the base implementation which comes from System.Object. If you inspect that codefile (.\sscli20\clr\src\bcl\system\object.cs) you will find the method is extern (see code below). Further inspect could uncover the implementation, but its not in the BCL. I suspect it will be in C++ code somewhere.

// Returns a Type object which represent this object instance.
// 
[MethodImplAttribute(MethodImplOptions.InternalCall)]
public extern Type GetType();

UPDATE (AGAIN): I dug deeper and found the answer in the implementation of the CLR virtual machine itself. (Its in C++).

The first piece of puzzle is here:

\sscli20\clr\src\vm\ecall.cpp

Here we see the code that maps the external call to an C++ function.

FCFuncStart(gObjectFuncs)
    FCIntrinsic("GetType", ObjectNative::GetClass, CORINFO_INTRINSIC_Object_GetType)
    FCFuncElement("InternalGetHashCode", ObjectNative::GetHashCode)
    FCFuncElement("InternalEquals", ObjectNative::Equals)
    FCFuncElement("MemberwiseClone", ObjectNative::Clone)
FCFuncEnd()

Now, we need to go find ObjectNative::GetClass ... which is here:

\sscli20\clr\src\vm\comobject.cpp

and here is the implementation of GetType:

    FCIMPL1(Object*, ObjectNative::GetClass, Object* pThis)
{
    CONTRACTL
    {
        THROWS;
        SO_TOLERANT;
        DISABLED(GC_TRIGGERS); // FCallCheck calls ForbidenGC now
        INJECT_FAULT(FCThrow(kOutOfMemoryException););
        SO_TOLERANT;
        MODE_COOPERATIVE;
    }
    CONTRACTL_END;

    OBJECTREF   objRef   = ObjectToOBJECTREF(pThis);
    OBJECTREF   refType  = NULL;
    TypeHandle  typeHandle = TypeHandle();

    if (objRef == NULL) 
        FCThrow(kNullReferenceException);

    typeHandle = objRef->GetTypeHandle();
    if (typeHandle.IsUnsharedMT())
        refType = typeHandle.AsMethodTable()->GetManagedClassObjectIfExists();
    else
        refType = typeHandle.GetManagedClassObjectIfExists();

    if (refType != NULL)
        return OBJECTREFToObject(refType);

    HELPER_METHOD_FRAME_BEGIN_RET_ATTRIB_2(Frame::FRAME_ATTR_RETURNOBJ, objRef, refType);

    if (!objRef->IsThunking())
        refType = typeHandle.GetManagedClassObject();
    else
        refType = CRemotingServices::GetClass(objRef);
    HELPER_METHOD_FRAME_END();

    return OBJECTREFToObject(refType);
}
FCIMPLEND

One last thing, the implementation of GetTypeHandle along with some other supporting functions can be found in here:

\sscli20\clr\src\vm\object.cpp