I like the technique to generate compile error when there is a mismatch between format string and actual argument list and type - This is what only statically typed language can do and dynamically typed languages like python can't do.

Maybe this technique could be applied in printf or other C++ APIs using format string.

Not sure if you're being ironic, but you're describing e.g. GCC's "format" function attribute (https://gcc.gnu.org/onlinedocs/gcc/Function-Attributes.html#...), it makes the compiler verify the arguments for printf() and other format-string functions.

It's not new, it has been in GCC for quite a number of years (not sure how to check this quickly).

UPDATE: I found a list (https://ohse.de/uwe/articles/gcc-attributes.html#func-format) that says format was added in GCC 2.3-3.4 (whatever the range means). GCC 3.4.0 was released on April 18 2004. Now I'm sad I didn't say "ten years" above, as my original hunch was. :)

Specific to printf and scanf format codes though, not under the control of the programmer.

boost::format does away with format codes altogether... you just use '%' place holders. Using constexpr string literal evaluation would be useful for counting them at compile time though.

A friend of mine is recently writing C++ web framework similar to Python Flask.

It has many interesting features like compile-time routing URL parameter checking, easy and fast (probably fastest among C++ json libs) json implementation by taking full advantage of C++11. If interested, take look of following code and repository:

https://github.com/ipkn/crow/blob/master/example.cpp

This actually looks pretty awesome :)