How call function on Err arm - rust

Question

I wrote this code and it works. But I have a custom class for outputting logs to stdout. I want to call my logging function if I get an Error instead of panic! macro.
fn create_logfile() -> File {
let timestamp = Log::format_date(chrono::Local::now());
let filename = format!("{}.log", timestamp);
let logfile = match File::create(filename) {
Ok(file) => file,
Err(error) => {
panic!("There was a problem creating the file: {:?}", error)
}
};
logfile
}
For example I want get something like that:
let logfile = match File::create(filename) {
Ok(file) => file,
Err(e) => {
Log::error("Log file creation failed, reason: {}", e);
process::exit(1)
}
};
But compiler says:
[E0308] `match` arms have incompatible types.
[Note] expected struct `File`, found `()
How can I solve this problem?
If I put the error data to stderr will it help?

Answer 1

Your revised example with std::process::exit() works for me: (link)
use chrono; // 0.4.23
use std::fs::File;
use log; // 0.4.17
struct Log { }
impl Log {
fn format_date(date: chrono::DateTime<chrono::offset::Local>) -> i64 {
return 0;
}
}
fn old_create_logfile() -> File {
let timestamp = Log::format_date(chrono::Local::now());
let filename = format!("{}.log", timestamp);
let logfile = match File::create(filename) {
Ok(file) => file,
Err(error) => {
panic!("There was a problem creating the file: {:?}", error)
}
};
logfile
}
fn new_create_logfile() -> File {
let timestamp = Log::format_date(chrono::Local::now());
let filename = format!("{}.log", timestamp);
let logfile = match File::create(filename) {
Ok(file) => file,
Err(e) => {
// Instead of using `Log::error`, we'll use `log::error!` for show.
log::error!("Log file creation failed, reason: {}", e);
// This compiles.
std::process::exit(1)
}
};
logfile
}
fn main() {
new_create_logfile();
}
Normally, you need to make sure the return types of all match arms have the same type -- here, you are returning std::fs::File under the Ok branch, so the Err branch can "escape" the requirement by returning ! (pronounced "never") (link).
Since computation never returns from the std::process::exit() and its return type is marked as !, it's passes the type-checking stage.