size of a string in bytes

[Nestor via Digitalmars-d-learn]

Hi,

One can get the length of a string easily, however since strings 
are UTF-8, sometimes characters take more than one byte. I would 
like to know then how many bytes does a string take, but this 
code didn't work as I expected:

import std.stdio;
void main() {
   string mystring1;
   string mystring2 = "A string of just 48 characters for testing 
size.";
   writeln(mystring1.sizeof);
   writeln( mystring2.sizeof);
}

In both cases the size is 8, so apparently sizeof is giving me 
just the default size of a string type and not the size of the 
variable in memory, which is what I want.

Ideas?