How to convert this code: (is(ToString(t))

[Pablo via Digitalmars-d]

This is part of the old dparse.d file:

private import std.string : ToString = toString ;
        char[] string()
        {
                static if(str)
                {
                        static if(is(T == char[]))
                                return t;
                        else static if(is(ToString(t)))
                                return ToString(t);
                        else
                                return "<<"~T.stringof~">>";
                }
                else
                        return "<<"~T.stringof~">>";
        }

I have a problem with this part:  (is(ToString(t)) :
dparse.d(215): Error: function declaration without return type. 
(Note that constructors are always named 'this')

How to fix this code?

Regards
Pawel