Struct std::panic::AssertUnwindSafe
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pub struct AssertUnwindSafe<T>(pub T);1.9.0
A simple wrapper around a type to assert that it is panic safe.
When using recover it may be the case that some of the closed over
variables are not panic safe. For example if &mut T is captured the
compiler will generate a warning indicating that it is not panic safe. It
may not be the case, however, that this is actually a problem due to the
specific usage of recover if panic safety is specifically taken into
account. This wrapper struct is useful for a quick and lightweight
annotation that a variable is indeed panic safe.
Examples
One way to use AssertUnwindSafe is to assert that the entire closure
itself is recover safe, bypassing all checks for all variables:
use std::panic::{self, AssertUnwindSafe}; let mut variable = 4; // This code will not compile because the closure captures `&mut variable` // which is not considered panic safe by default. // panic::catch_unwind(|| { // variable += 3; // }); // This, however, will compile due to the `AssertUnwindSafe` wrapper let result = panic::catch_unwind(AssertUnwindSafe(|| { variable += 3; })); // ...
Wrapping the entire closure amounts to a blanket assertion that all captured variables are unwind safe. This has the downside that if new captures are added in the future, they will also be considered unwind safe. Therefore, you may prefer to just wrap individual captures, as shown below. This is more annotation, but it ensures that if a new capture is added which is not unwind safe, you will get a compilation error at that time, which will allow you to consider whether that new capture in fact represent a bug or not.
fn main() { use std::panic::{self, AssertUnwindSafe}; let mut variable = 4; let other_capture = 3; let result = { let mut wrapper = AssertUnwindSafe(&mut variable); panic::catch_unwind(move || { **wrapper += other_capture; }) }; // ... }use std::panic::{self, AssertUnwindSafe}; let mut variable = 4; let other_capture = 3; let result = { let mut wrapper = AssertUnwindSafe(&mut variable); panic::catch_unwind(move || { **wrapper += other_capture; }) }; // ...