$ cat xor.d import std.random; import std.stdio; int main() { Random r = Random(); writefln(r.front); return 0; } $ dmd xor.d /dmd/linux/bin/../../src/phobos/std/stdio.d(511): Error: template std.format.formattedWrite(Writer,F,A...) does not match any function template declaration /dmd/linux/bin/../../src/phobos/std/stdio.d(511): Error: template std.format.formattedWrite(Writer,F,A...) cannot deduce template function from argument types !()(LockingTextWriter,uint)
The bug is already fixed -- recent Phobos generates following error message for your testcase: Error: static assert "You must pass a formatting string as the first argument to writef or writefln. If no formatting is needed, you may want to use write or writeln."