> Maybe I'm spoiled by other languages with more powerful type systems, but this is exactly what I want my types to do! Isn't this why we have type traits and concepts and whatnot in C++ now? If not for semantics, why have types at all, the compiler could figure out what amount of bytes it needs to store my data in, after all.

yes, but understand that, despite the name, what unsigned models in C / C++ is not "positive numbers" but "modulo 2^N" arithmetic (while signed models the usual arithmetic).

There is no good type that says "always positive" by default in C or C++ - any type which gives you an infinite loop if you do

    for({int,unsigned,whatever} i = 0; i < n - 1; i++) {
       // oops, n was zero, n - 1 is 4.something billion, see you tomorrow
    }

is not a good type.

If you want a "always positive" type use some safe_int template such as https://github.com/dcleblanc/SafeInt - here if you do "x - y" and the result of the computation should be negative, then you'll get the rightful runtime error that you want, not some arbitrarily high and incorrect number

The correct uses of unsigned are for instance for computations of hashes, crypto algorithms, random number generation, etc... as those are in general defined in modular arithmetic