a delegate used to sink character arrays;
$(PHOBOS format, FormatException, FormatException) if the format specifier is not supported
$(PHOBOS format, FormatSpec, FormatSpec) $(PHOBOS format, format, format) $(PHOBOS conv, to, to) $(PHOBOS stdio, writef, writef) $(PHOBOS stdio, writefln, writefln)
Converts current value to string, passing it to the given sink using the specified format.