std.file vs std.stream

[Ludovic A.]

I am trying to write a simple file parser in D2. Following examples I found 2
working ways to read a line and print it:

import std.stream
(...)
  Stream file = new BufferedFile(filename);
  foreach(char[] line; file)
  {
    writefln("line: %s",line);
  }

OR

import std.file;
(...)
File* file = new File(filename);
   while (!file.eof())
   {
     writef("%s", file.readln());
   }

My question from there is what is the difference between opening a stream and
a file _in this case_, and what is the most appropriate in this case?

Also in the foreach I can not write foreach (string line, file) but I have to
use char[]. Is there a way to go around this?

Finally I can not use foreach in the std.file example, because the compiler
says "foreach: File* is not an aggregate type". I was surprised that foreach
worked on a Stream at the first place, so no big deal :) But what do we have
under the hood? How can it work for Stream and not for File? Is the limitation
coming from the foreach implementation?