# Struct std::panic::AssertUnwindSafe

1.9.0 · source ·

    pub struct AssertUnwindSafe<T>(pub T);

Expand description

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 might 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

## Tuple Fields§

§`0: T`

## Trait Implementations§

source§

### impl<S> AsyncIterator for AssertUnwindSafe<S>where S: AsyncIterator,

§

#### type Item = <S as AsyncIterator>::Item

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
The type of items yielded by the async iterator.
source§

#### fn poll_next( self: Pin<&mut AssertUnwindSafe<S>>, cx: &mut Context<'_> ) -> Poll<Option<<S as AsyncIterator>::Item>>

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
Attempt to pull out the next value of this async iterator, registering the current task for wakeup if the value is not yet available, and returning `None` if the async iterator is exhausted. Read more
source§

#### fn size_hint(&self) -> (usize, Option<usize>)

🔬This is a nightly-only experimental API. (`async_iterator` #79024)
Returns the bounds on the remaining length of the async iterator. Read more
1.16.0 · source§

### impl<T> Debug for AssertUnwindSafe<T>where T: Debug,

source§

#### fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter. Read more
1.62.0 · source§

### impl<T> Default for AssertUnwindSafe<T>where T: Default,

source§

#### fn default() -> AssertUnwindSafe<T> ⓘ

Returns the “default value” for a type. Read more
source§

### impl<T> Deref for AssertUnwindSafe<T>

§

#### type Target = T

The resulting type after dereferencing.
source§

#### fn deref(&self) -> &T

Dereferences the value.
source§

### impl<T> DerefMut for AssertUnwindSafe<T>

source§

#### fn deref_mut(&mut self) -> &mut T

Mutably dereferences the value.
source§

### impl<R, F> FnOnce() for AssertUnwindSafe<F>where F: FnOnce() -> R,

§

#### type Output = R

The returned type after the call operator is used.
source§

#### extern "rust-call" fn call_once(self, _args: ()) -> R

🔬This is a nightly-only experimental API. (`fn_traits` #29625)
Performs the call operation.
1.36.0 · source§

### impl<F> Future for AssertUnwindSafe<F>where F: Future,

§

#### type Output = <F as Future>::Output

The type of value produced on completion.
source§

#### fn poll( self: Pin<&mut AssertUnwindSafe<F>>, cx: &mut Context<'_> ) -> Poll<<AssertUnwindSafe<F> as Future>::Output>

Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more
source§

### impl<T> RefUnwindSafe for AssertUnwindSafe<T>

source§

### impl<T> UnwindSafe for AssertUnwindSafe<T>

## Auto Trait Implementations§

§

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

§

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

§

### impl<T> Unpin for AssertUnwindSafe<T>where T: Unpin,

## Blanket Implementations§

source§

### impl<T> Any for Twhere T: 'static + ?Sized,

source§

#### fn type_id(&self) -> TypeId

Gets the `TypeId` of `self`. Read more
source§

### impl<T> Borrow<T> for Twhere T: ?Sized,

source§

#### fn borrow(&self) -> &T

Immutably borrows from an owned value. Read more
source§

### impl<T> BorrowMut<T> for Twhere T: ?Sized,

source§

#### fn borrow_mut(&mut self) -> &mut T

Mutably borrows from an owned value. Read more
source§

### impl<T> From<T> for T

source§

#### fn from(t: T) -> T

Returns the argument unchanged.

source§

### impl<T, U> Into<U> for Twhere U: From<T>,

source§

#### fn into(self) -> U

Calls `U::from(self)`.

That is, this conversion is whatever the implementation of `From<T> for U` chooses to do.

source§

### impl<F> IntoFuture for Fwhere F: Future,

§

#### type Output = <F as Future>::Output

The output that the future will produce on completion.
§

#### type IntoFuture = F

Which kind of future are we turning this into?
source§

#### fn into_future(self) -> <F as IntoFuture>::IntoFuture

Creates a future from a value. Read more
source§

### impl<T, U> TryFrom<U> for Twhere U: Into<T>,

§

#### type Error = Infallible

The type returned in the event of a conversion error.
source§

#### fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>

Performs the conversion.
source§

### impl<T, U> TryInto<U> for Twhere U: TryFrom<T>,

§

#### type Error = <U as TryFrom<T>>::Error

The type returned in the event of a conversion error.
source§

#### fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>

Performs the conversion.