Is it possible to pass a variable's name along with the value, when passing through functions? - vb.net

Question

I want to know if it's possible to retrieve the variables name from when it was passed into a certain function. For example, if I call parseId(myId) to a function with the signature parseId(id), i can obviously retrieve the value of 'id'. However, is there any way I can retrieve 'myId' as a string (without passing it as another value)?
Specifically in vb.net, but I'm interested in how it would work in any given language.

Answer 1

This is all just random thoughts.. feel free to dismiss or not ;-p
Re your comment about use with stored procedures... if you want to go that route, I wouldn't mess around with the local variable names; that is an implementation detail. However, you could expose those details on an interface method and use the names from there, since that is more formalised - for example (C#):
interface ICustomerRepository {
Customer GetById(int id); // perhaps an attribute to name the sproc
}
You can use similar expression-tree parsing (as discussed here) to get the name and value of the parameter, for example:
var repoWrapper = new Repo<ICustomerRepository>();
int custId = 12345;
var cust = repoWrapper.Execute(r => r.GetById(custId));
Here we'd want to resolve the argument to GetById as "id" (not "custId"), with value 12345. This is actually exactly what my protobuf-net RPC code does ;-p (just don't ask me to translate it to VB - it is hard enough to write it in a language you know well...)

Answer 2

No, you can't do that in the normal sense. What are you really trying to accomplish with this?

Answer 3

You can do this in .NET 3.5 and above using expression trees; I'll knock up a C# example, and try to run it through reflector for VB...
C#:
static void Main()
{
int i = 17;
WriteLine(() => i);
}
static void WriteLine<T>(Expression<Func<T>> expression)
{
string name;
switch (expression.Body.NodeType)
{
case ExpressionType.MemberAccess:
name = ((MemberExpression)expression.Body).Member.Name;
break;
default:
throw new NotSupportedException("Give me a chance!");
}
T val = expression.Compile()();
Console.WriteLine(name + "=" + val);
}
The VB is below, but note that the VB compiler seems to use different names (like $VB$Local_i, not i):
Sub Main()
Dim i As Integer = 17
WriteLine(Function() i)
End Sub
Private Sub WriteLine(Of T)(ByVal expression As Expression(Of Func(Of T)))
If (expression.Body.NodeType <> ExpressionType.MemberAccess) Then
Throw New NotSupportedException("Give me a chance!")
End If
Console.WriteLine((DirectCast(expression.Body, MemberExpression).Member.Name
& "=" & Convert.ToString(expression.Compile.Invoke)))
End Sub