# 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: Debug> Debug for AssertUnwindSafe<T>`1.16.0[src]

#### `pub fn fmt(&self, f: &mut Formatter<'_>) -> Result`[src]

Formats the value using the given formatter. Read more

### `impl<T> Deref for AssertUnwindSafe<T>`[src]

#### `type Target = T`

The resulting type after dereferencing.

#### `pub fn deref(&self) -> &Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`[src]

Dereferences the value.

### `impl<T> DerefMut for AssertUnwindSafe<T>`[src]

#### `pub fn deref_mut(&mut self) -> &mut Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`[src]

Mutably dereferences the value.

### `impl<R, F: FnOnce() -> R> FnOnce() for AssertUnwindSafe<F>`[src]

#### `type Output = R`

The returned type after the call operator is used.

#### `pub extern "rust-call" fn call_once(self, _args: ()) -> R`[src]

🔬 This is a nightly-only experimental API. (`fn_traits` #29625)

Performs the call operation.

### `impl<F: Future> Future for AssertUnwindSafe<F>`1.36.0[src]

#### `type Output = F::Output`

The type of value produced on completion.

#### `pub fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output>`[src]

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

### `impl<T> RefUnwindSafe for AssertUnwindSafe<T>`[src]

### `impl<T> UnwindSafe for AssertUnwindSafe<T>`[src]

## 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

### `impl<T> Any for T where
T: 'static + ?Sized,` [src]

#### `pub fn type_id(&self) -> TypeId`[src]

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

### `impl<T> Borrow<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow(&self) -> &Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`[src]

Immutably borrows from an owned value. Read more

### `impl<T> BorrowMut<T> for T where
T: ?Sized,` [src]

#### `pub fn borrow_mut(&mut self) -> &mut Tⓘ

### Notable traits for &'_ mut F

`impl<'_, F> Future for &'_ mut F where
F: Unpin + Future + ?Sized, type Output = <F as Future>::Output;impl<'_, I> Iterator for &'_ mut I where
I: Iterator + ?Sized, type Item = <I as Iterator>::Item;impl<R: Read + ?Sized, '_> Read for &'_ mut Rimpl<W: Write + ?Sized, '_> Write for &'_ mut W`
`[src]

Mutably borrows from an owned value. Read more

### `impl<T> From<T> for T`[src]

#### `pub fn from(t: T) -> T`[src]

Performs the conversion.

### `impl<T, U> Into<U> for T where
U: From<T>,` [src]

#### `pub fn into(self) -> U`[src]

Performs the conversion.

### `impl<F> IntoFuture for F where
F: Future,` [src]

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

🔬 This is a nightly-only experimental API. (`into_future` #67644)

The output that the future will produce on completion.

#### `type Future = F`

🔬 This is a nightly-only experimental API. (`into_future` #67644)

Which kind of future are we turning this into?

#### `pub fn into_future(self) -> <F as IntoFuture>::Future`[src]

🔬 This is a nightly-only experimental API. (`into_future` #67644)

Creates a future from a value.

### `impl<T, U> TryFrom<U> for T where
U: Into<T>,` [src]

#### `type Error = Infallible`

The type returned in the event of a conversion error.

#### `pub fn try_from(value: U) -> Result<T, <T as TryFrom<U>>::Error>`[src]

Performs the conversion.

### `impl<T, U> TryInto<U> for T where
U: TryFrom<T>,` [src]

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

The type returned in the event of a conversion error.

#### `pub fn try_into(self) -> Result<U, <U as TryFrom<T>>::Error>`[src]

Performs the conversion.