Rust, make action after panic - rust

Question

I have question about make action after panic!. I have strong experience with python, and often I use:
try:
do_something()
exception:
do_something_else()
But can't do that in Rust. My code is bellow:
fn do_something(value: u32) -> Result<u32, io::Error> {
if value > 30 {
panic!("Value is bigger then 30!");
}
else {
Ok(value)
}
}
// first try
fn if_else_catch(value: u32) -> Result<u32, u32> {
let result = do_something(value);
let something = match result {
Ok(something) => something + something,
Err(err) => do_something_else(),
};
Ok(something)
}
fn if_else_catch_retun_different_value(value: u32) -> Result<u32, u32> {
let result = do_something(value);
let something = match result {
Ok(something) => something + something,
Err(err) => 100,
};
Ok(something)
}
// another try
fn do_something_else_with_questionmark(value: u32) -> Result<u32, io::Error> {
let result = do_something(value)?;
if let Err(_err) = do_something(value) {
println!("An Error occured!");
}
Ok(result)
}
fn main() {
println!("Do something: {}", do_something(35).unwrap());
println!("Do something res: {}", if_else_catch(35).unwrap());
}
Is it possible to do this?
How can I implement it?
I already check documentation, but example like this:
let greeting_file_result = File::open("hello.txt");
let greeting_file = match greeting_file_result {
Ok(file) => file,
Err(error) => panic!("Problem opening the file: {:?}", error),
};
^
|
Doesn't work for this case.

Answer 1

The natural thing would be to just return an Err in your error case:
use std::io::{Error, ErrorKind};
fn do_something(value: u32) -> Result<u32, Error> {
if value > 30 {
Err(Error::new(ErrorKind::Other, "Value is bigger than 30!"))
} else {
Ok(value)
}
}
If you really have to you can use catch_unwind to recover from panics but
It is not recommended to use this function for a general try/catch mechanism. The Result type is more appropriate to use for functions that can fail on a regular basis. Additionally, this function is not guaranteed to catch all panics.
use std::panic::catch_unwind;
fn catch_it(value: u32) -> Result<u32, u32> {
let result = catch_unwind(|| do_something(value));
let something = match result {
Ok(Ok(something)) => something + something,
Ok(Err(_)) | Err(_) => do_something_else(),
};
Ok(something)
}