71 lines
1.8 KiB
Rust
71 lines
1.8 KiB
Rust
|
// Go's defer in Rust, with error value return.
|
||
|
|
|
||
|
|
use std::rc::Rc;
|
||
|
|
use std::sync::RwLock;
|
||
|
|
|
||
|
|
struct Defer<F: Fn()> {
|
||
|
|
f: F
|
||
|
|
}
|
||
|
|
|
||
|
|
impl <F: Fn()> Drop for Defer<F> {
|
||
|
|
fn drop(&mut self) {
|
||
|
|
(self.f)()
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
// Only added this for Go-syntax familiarity ;-)
|
||
|
|
fn defer<F: Fn()>(f: F) -> Defer<F> {
|
||
|
|
Defer { f }
|
||
|
|
}
|
||
|
|
|
||
|
|
// Convenience type synonym. This is a reference-counted smart pointer to
|
||
|
|
// a shareable, mutable variable.
|
||
|
|
// Rust does not allow willy-nilly mutation of shared variables, so explicit
|
||
|
|
// write-locking must be performed.
|
||
|
|
type ErrorHandle<T> = Rc<RwLock<Option<T>>>;
|
||
|
|
|
||
|
|
///////////////////
|
||
|
|
// Usage example //
|
||
|
|
///////////////////
|
||
|
|
|
||
|
|
#[derive(Debug)] // Debug trait for some default way to print the type.
|
||
|
|
enum Error { DropError }
|
||
|
|
|
||
|
|
fn main() {
|
||
|
|
// Create a place to store the error.
|
||
|
|
let drop_err: ErrorHandle<Error> = Default::default(); // create empty error
|
||
|
|
|
||
|
|
// Introduce an arbitrary scope block (so that we still have control after
|
||
|
|
// the defer runs):
|
||
|
|
{
|
||
|
|
let mut i = 1;
|
||
|
|
|
||
|
|
// Rc types are safe to clone and share for multiple ownership.
|
||
|
|
let err_handle = drop_err.clone();
|
||
|
|
|
||
|
|
// Call defer and let the closure own the cloned handle to the error:
|
||
|
|
let token = defer(move || {
|
||
|
|
// do something!
|
||
|
|
println!("Value is: {}", i);
|
||
|
|
|
||
|
|
// ... oh no, it went wrong!
|
||
|
|
*err_handle.write().unwrap() = Some(Error::DropError);
|
||
|
|
});
|
||
|
|
|
||
|
|
i += 1;
|
||
|
|
println!("Value is: {}", i);
|
||
|
|
|
||
|
|
// token goes out of scope here - drop() is called.
|
||
|
|
}
|
||
|
|
|
||
|
|
match *drop_err.read().unwrap() {
|
||
|
|
Some(ref err) => println!("Oh no, an error occured: {:?}!", err),
|
||
|
|
None => println!("Phew, everything went well.")
|
||
|
|
};
|
||
|
|
}
|
||
|
|
|
||
|
|
// Prints:
|
||
|
|
// Value is: 2
|
||
|
|
// Value is: 1
|
||
|
|
// Oh no, an error occured: DropError!
|