From: Ábel Sinkovics
The typesafe printf is important because it is more than a table-based regexp recogniser. It builds an MPL list of expected types by parsing the format string and type-checks the printf arguments using it. Thus, it demonstrates that you have full access to template metaprogramming while you're parsing.
Syntax example: printf<_S("John %d, %s %d\n")>(11, "Joe", 13); Yay! That syntax doesn't suck. The _S would be BOOST_S if it were a boost library, I guess, or perhaps BOOST_MPL_STRING if we want to be very descriptive. Too bad we need the macro. It would be nice to jet get a variadic template instantiation from the language if we wrote printf<"John %d, %s, %d\n"> directly. It is pretty obvious that we can take this idea and run with it to do something really evil like: ruby<_S("_1.each {|item| puts item }")>(my_array); or perl<_S("foreach $item (@_1){ print "$item\n"; }")>(my_array); Man is that evil. Right up there with overloading the comma operator evilness. Ok, now, hands please, who wants to implement a Ruby interpreter as a template metaprogram? Laughing evilly yours, Luke