1.9.0[][src]Struct std::panic::AssertUnwindSafe

pub struct AssertUnwindSafe<T>(pub T);

A simple wrapper around a type to assert that it is unwind safe.

When using catch_unwind it may be the case that some of the closed over variables are not unwind safe. For example if &mut T is captured the compiler will generate a warning indicating that it is not unwind safe. It may not be the case, however, that this is actually a problem due to the specific usage of catch_unwind if unwind safety is specifically taken into account. This wrapper struct is useful for a quick and lightweight annotation that a variable is indeed unwind safe.

Examples

One way to use AssertUnwindSafe is to assert that the entire closure itself is unwind 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 unwind 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;
}));
// ...Run

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.

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;
    })
};
// ...Run

Trait Implementations

impl<T> UnwindSafe for AssertUnwindSafe<T>
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impl<T> RefUnwindSafe for AssertUnwindSafe<T>
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impl<T: Debug> Debug for AssertUnwindSafe<T>
1.16.0
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impl<T> Deref for AssertUnwindSafe<T>
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The resulting type after dereferencing.

impl<T> DerefMut for AssertUnwindSafe<T>
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impl<R, F: FnOnce() -> R> FnOnce() for AssertUnwindSafe<F>
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The returned type after the call operator is used.

impl<'a, F: Future> Future for AssertUnwindSafe<F>
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🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

The result of the Future.

Auto Trait Implementations

impl<T> Send for AssertUnwindSafe<T> where
    T: Send

impl<T> Sync for AssertUnwindSafe<T> where
    T: Sync

Blanket Implementations

impl<T, U> TryFrom for T where
    T: From<U>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T> From for T
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impl<T, U> TryInto for T where
    U: TryFrom<T>, 
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🔬 This is a nightly-only experimental API. (try_from #33417)

The type returned in the event of a conversion error.

impl<T, U> Into for T where
    U: From<T>, 
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impl<T> Borrow for T where
    T: ?Sized
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impl<T> BorrowMut for T where
    T: ?Sized
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impl<T> Any for T where
    T: 'static + ?Sized
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impl<A, F> FnBox for F where
    F: FnOnce<A>, 
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🔬 This is a nightly-only experimental API. (fnbox #28796)

will be deprecated if and when Box<FnOnce> becomes usable