You can write a Rust function that returns `i32` where a negative value indicates an error case. Nothing in Rust prevents you from doing that. But Rust does have facilities that may offer a nicer way of solving your underlying problem.
For instance, a common example of the "integer on error" pattern in other languages is `array.index_of(element)`, returning a non-negative index if found or a negative value if not found. In Rust, the return type of `Iterator::position` is instead `Option<usize>`. You can't accidentally forget to check whether it's present. You could still write your own `index_of(&self, element: &T) -> isize /* negative if not found */` if that's your preference.
For instance, a common example of the "integer on error" pattern in other languages is `array.index_of(element)`, returning a non-negative index if found or a negative value if not found. In Rust, the return type of `Iterator::position` is instead `Option<usize>`. You can't accidentally forget to check whether it's present. You could still write your own `index_of(&self, element: &T) -> isize /* negative if not found */` if that's your preference.
https://doc.rust-lang.org/std/iter/trait.Iterator.html#metho...