> like using `fn` for functions and `->` to annotate return types `->` syntax is included in C++11 standard, named "trailing return type", but its adoption see

> like using `fn` for functions and `->` to annotate return types `->` syntax is included in C++11 standard, named "trailing return type", but its adoption seems to be very slow. `auto f() -> int { return 42; }`