``` #include <stdio.h>

typedef struct { int value; } Feet;

typedef struct { int value; } Meters;

void hover(Meters altitude) { printf("At %i meters\n", altitude.value); }

int main() { Meters altitude1 = {.value = 16}; hover(altitude1); Feet altitude2 = {.value = 16}; hover(altitude2); } ```

``` error: passing 'Feet' to parameter of incompatible type 'Meters' 20 | hover(altitude2); ```

Coming from a dynamically typed language (Python, etc), this might seem like a revelation, but its old news since the dawn of programming computers. A C language server will pick this up before compile time, just like `rust-analyzer` does: `argument of type "Feet" is incompatible with parameter of type "Meters"`.

Did you not know this? I feel like a lot of people on message boards criticizing C don't know that this would fail to compile and the IDE would tell you in advance...

In C++ you can even add overloaded operators to make using math on such structs ergonomical.

Compilers know of the idiom, and will optimize the struct away.

> An investigation attributed the failure to a measurement mismatch between two measurement systems: SI units (metric) by NASA and US customary units by spacecraft builder Lockheed Martin.[3]

IIUC, rust would NOT let you do a type checked m/s * s => m, so using the type system for these kinds of games is silly and dangerous (I presume you would have to do the dumb thing and typeconvert to the same type -- e.g.

    (m) (speed * ((m/s) seconds))

[1] https://github.com/helsing-ai/sguaba

I haven't written rust, but my impression is the benefit is more about deeper introspection of things like lifetime than basic typesafety, which already exists in C/C++ (and is likewise occasionally bypassed for convenience, so I wonder how often the same is done for Rust)

/s