a function like writeln that returns a string rather than writes to a file

[dan]

I'm looking for a function something like writeln or write, but 
instead of writing to stdout, it writes to a string and returns 
the string.

So i would like something like:

import std.stdio;
import std.conv;

string write_to_string(T...)(T values ) {
   string s;
   foreach ( value; values ) s ~= to!string( value );
   return s;
}

But because this is such a standard type of thing to do, i'd like 
to use whatever the standard function is for doing it, if there 
is one.

So . . . is there one?  Like maybe some way to dress a string up 
as a file and pass it through the usual write/writeln apparatus?  
My only real requirement is that it be something really easy to 
do.

Thanks in advance for any pointers.

dan