f() + g();

What happens if f and g touch the same bit of state?

• In Rust, this is perfectly valid, and f runs strictly before g.

• In C, this construct is not legal - it is ‘undefined behaviour.’ Your compiler won’t (can’t) disallow it, but it is allowed to assume that it never happens.

This means that theoretically, a C compiler is allowed to automatically parallelize this code, but in Rust, we must wait for f to complete before g is able to run.

Enjoy the rest of your day.