1.0.0[][src]Struct alloc::boxed::Box

#[lang = "owned_box"]
pub struct Box<T: ?Sized>(_);

A pointer type for heap allocation.

See the module-level documentation for more.

Methods

impl<T> Box<T>
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Important traits for Box<I>

Allocates memory on the heap and then places x into it.

This doesn't actually allocate if T is zero-sized.

Examples

let five = Box::new(5);

impl<T: ?Sized> Box<T>
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Constructs a box from a raw pointer.

After calling this function, the raw pointer is owned by the resulting Box. Specifically, the Box destructor will call the destructor of T and free the allocated memory. Since the way Box allocates and releases memory is unspecified, the only valid pointer to pass to this function is the one taken from another Box via the Box::into_raw function.

This function is unsafe because improper use may lead to memory problems. For example, a double-free may occur if the function is called twice on the same raw pointer.

Examples

let x = Box::new(5);
let ptr = Box::into_raw(x);
let x = unsafe { Box::from_raw(ptr) };

Consumes the Box, returning a wrapped raw pointer.

The pointer will be properly aligned and non-null.

After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory. The proper way to do so is to convert the raw pointer back into a Box with the Box::from_raw function.

Note: this is an associated function, which means that you have to call it as Box::into_raw(b) instead of b.into_raw(). This is so that there is no conflict with a method on the inner type.

Examples

let x = Box::new(5);
let ptr = Box::into_raw(x);

🔬 This is a nightly-only experimental API. (box_into_raw_non_null #47336)

Consumes the Box, returning the wrapped pointer as NonNull<T>.

After calling this function, the caller is responsible for the memory previously managed by the Box. In particular, the caller should properly destroy T and release the memory. The proper way to do so is to convert the NonNull<T> pointer into a raw pointer and back into a Box with the Box::from_raw function.

Note: this is an associated function, which means that you have to call it as Box::into_raw_non_null(b) instead of b.into_raw_non_null(). This is so that there is no conflict with a method on the inner type.

Examples

#![feature(box_into_raw_non_null)]

fn main() {
    let x = Box::new(5);
    let ptr = Box::into_raw_non_null(x);
}

Consumes and leaks the Box, returning a mutable reference, &'a mut T. Note that the type T must outlive the chosen lifetime 'a. If the type has only static references, or none at all, then this may be chosen to be 'static.

This function is mainly useful for data that lives for the remainder of the program's life. Dropping the returned reference will cause a memory leak. If this is not acceptable, the reference should first be wrapped with the Box::from_raw function producing a Box. This Box can then be dropped which will properly destroy T and release the allocated memory.

Note: this is an associated function, which means that you have to call it as Box::leak(b) instead of b.leak(). This is so that there is no conflict with a method on the inner type.

Examples

Simple usage:

fn main() {
    let x = Box::new(41);
    let static_ref: &'static mut usize = Box::leak(x);
    *static_ref += 1;
    assert_eq!(*static_ref, 42);
}

Unsized data:

fn main() {
    let x = vec![1, 2, 3].into_boxed_slice();
    let static_ref = Box::leak(x);
    static_ref[0] = 4;
    assert_eq!(*static_ref, [4, 2, 3]);
}

impl Box<Any>
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Attempt to downcast the box to a concrete type.

Examples

use std::any::Any;

fn print_if_string(value: Box<Any>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

fn main() {
    let my_string = "Hello World".to_string();
    print_if_string(Box::new(my_string));
    print_if_string(Box::new(0i8));
}

impl Box<Any + Send>
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Attempt to downcast the box to a concrete type.

Examples

use std::any::Any;

fn print_if_string(value: Box<Any + Send>) {
    if let Ok(string) = value.downcast::<String>() {
        println!("String ({}): {}", string.len(), string);
    }
}

fn main() {
    let my_string = "Hello World".to_string();
    print_if_string(Box::new(my_string));
    print_if_string(Box::new(0i8));
}

Trait Implementations

impl<T: ?Sized> Drop for Box<T>
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Executes the destructor for this type. Read more

impl<T: Default> Default for Box<T>
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Important traits for Box<I>

Creates a Box<T>, with the Default value for T.

impl<T> Default for Box<[T]>
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Important traits for Box<I>

Returns the "default value" for a type. Read more

impl Default for Box<str>
1.17.0
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Important traits for Box<I>

Returns the "default value" for a type. Read more

impl<T: Clone> Clone for Box<T>
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Important traits for Box<I>

Returns a new box with a clone() of this box's contents.

Examples

let x = Box::new(5);
let y = x.clone();

Copies source's contents into self without creating a new allocation.

Examples

let x = Box::new(5);
let mut y = Box::new(10);

y.clone_from(&x);

assert_eq!(*y, 5);

impl Clone for Box<str>
1.3.0
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<T: ?Sized + PartialEq> PartialEq for Box<T>
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This method tests for self and other values to be equal, and is used by ==. Read more

This method tests for !=.

impl<T: ?Sized + PartialOrd> PartialOrd for Box<T>
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This method returns an ordering between self and other values if one exists. Read more

This method tests less than (for self and other) and is used by the < operator. Read more

This method tests less than or equal to (for self and other) and is used by the <= operator. Read more

This method tests greater than or equal to (for self and other) and is used by the >= operator. Read more

This method tests greater than (for self and other) and is used by the > operator. Read more

impl<T: ?Sized + Ord> Ord for Box<T>
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This method returns an Ordering between self and other. Read more

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

impl<T: ?Sized + Eq> Eq for Box<T>
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impl<T: ?Sized + Hash> Hash for Box<T>
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Feeds this value into the given [Hasher]. Read more

Feeds a slice of this type into the given [Hasher]. Read more

impl<T: ?Sized + Hasher> Hasher for Box<T>
1.22.0
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Returns the hash value for the values written so far. Read more

Writes some data into this Hasher. Read more

Writes a single u8 into this hasher.

Writes a single u16 into this hasher.

Writes a single u32 into this hasher.

Writes a single u64 into this hasher.

Writes a single u128 into this hasher.

Writes a single usize into this hasher.

Writes a single i8 into this hasher.

Writes a single i16 into this hasher.

Writes a single i32 into this hasher.

Writes a single i64 into this hasher.

Writes a single i128 into this hasher.

Writes a single isize into this hasher.

impl<T> From<T> for Box<T>
1.6.0
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Performs the conversion.

impl<'a, T: Copy> From<&'a [T]> for Box<[T]>
1.17.0
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Important traits for Box<I>

Performs the conversion.

impl<'a> From<&'a str> for Box<str>
1.17.0
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Important traits for Box<I>

Performs the conversion.

impl From<Box<str>> for Box<[u8]>
1.19.0
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Performs the conversion.

impl<T: Display + ?Sized> Display for Box<T>
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Formats the value using the given formatter. Read more

impl<T: Debug + ?Sized> Debug for Box<T>
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Formats the value using the given formatter. Read more

impl<T: ?Sized> Pointer for Box<T>
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Formats the value using the given formatter.

impl<T: ?Sized> Deref for Box<T>
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The resulting type after dereferencing.

Dereferences the value.

impl<T: ?Sized> DerefMut for Box<T>
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Mutably dereferences the value.

impl<I: Iterator + ?Sized> Iterator for Box<I>
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The type of the elements being iterated over.

Advances the iterator and returns the next value. Read more

Returns the bounds on the remaining length of the iterator. Read more

Returns the nth element of the iterator. Read more

Consumes the iterator, counting the number of iterations and returning it. Read more

Consumes the iterator, returning the last element. Read more

Important traits for StepBy<I>

Creates an iterator starting at the same point, but stepping by the given amount at each iteration. Read more

Important traits for Chain<A, B>

Takes two iterators and creates a new iterator over both in sequence. Read more

Important traits for Zip<A, B>

'Zips up' two iterators into a single iterator of pairs. Read more

Important traits for Map<I, F>

Takes a closure and creates an iterator which calls that closure on each element. Read more

Calls a closure on each element of an iterator. Read more

Important traits for Filter<I, P>

Creates an iterator which uses a closure to determine if an element should be yielded. Read more

Important traits for FilterMap<I, F>

Creates an iterator that both filters and maps. Read more

Important traits for Enumerate<I>

Creates an iterator which gives the current iteration count as well as the next value. Read more

Important traits for Peekable<I>

Creates an iterator which can use peek to look at the next element of the iterator without consuming it. Read more

Important traits for SkipWhile<I, P>

Creates an iterator that [skip]s elements based on a predicate. Read more

Important traits for TakeWhile<I, P>

Creates an iterator that yields elements based on a predicate. Read more

Important traits for Skip<I>

Creates an iterator that skips the first n elements. Read more

Important traits for Take<I>

Creates an iterator that yields its first n elements. Read more

Important traits for Scan<I, St, F>

An iterator adaptor similar to [fold] that holds internal state and produces a new iterator. Read more

Important traits for FlatMap<I, U, F>

Creates an iterator that works like map, but flattens nested structure. Read more

Important traits for Flatten<I>

Creates an iterator that flattens nested structure. Read more

Important traits for Fuse<I>

Creates an iterator which ends after the first [None]. Read more

Important traits for Inspect<I, F>

Do something with each element of an iterator, passing the value on. Read more

Borrows an iterator, rather than consuming it. Read more

Transforms an iterator into a collection. Read more

Consumes an iterator, creating two collections from it. Read more

An iterator method that applies a function as long as it returns successfully, producing a single, final value. Read more

An iterator method that applies a fallible function to each item in the iterator, stopping at the first error and returning that error. Read more

An iterator method that applies a function, producing a single, final value. Read more

Tests if every element of the iterator matches a predicate. Read more

Tests if any element of the iterator matches a predicate. Read more

Searches for an element of an iterator that satisfies a predicate. Read more

Applies function to the elements of iterator and returns the first non-none result. Read more

Searches for an element in an iterator, returning its index. Read more

Searches for an element in an iterator from the right, returning its index. Read more

Returns the maximum element of an iterator. Read more

Returns the minimum element of an iterator. Read more

Returns the element that gives the maximum value from the specified function. Read more

Returns the element that gives the maximum value with respect to the specified comparison function. Read more

Returns the element that gives the minimum value from the specified function. Read more

Returns the element that gives the minimum value with respect to the specified comparison function. Read more

Important traits for Rev<I>

Reverses an iterator's direction. Read more

Converts an iterator of pairs into a pair of containers. Read more

Important traits for Cloned<I>

Creates an iterator which [clone]s all of its elements. Read more

Important traits for Cycle<I>

Repeats an iterator endlessly. Read more

Sums the elements of an iterator. Read more

Iterates over the entire iterator, multiplying all the elements Read more

Lexicographically compares the elements of this Iterator with those of another. Read more

Lexicographically compares the elements of this Iterator with those of another. Read more

Determines if the elements of this Iterator are equal to those of another. Read more

Determines if the elements of this Iterator are unequal to those of another. Read more

Determines if the elements of this Iterator are lexicographically less than those of another. Read more

Determines if the elements of this Iterator are lexicographically less or equal to those of another. Read more

Determines if the elements of this Iterator are lexicographically greater than those of another. Read more

Determines if the elements of this Iterator are lexicographically greater than or equal to those of another. Read more

impl<I: DoubleEndedIterator + ?Sized> DoubleEndedIterator for Box<I>
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Removes and returns an element from the end of the iterator. Read more

This is the reverse version of [try_fold()]: it takes elements starting from the back of the iterator. Read more

An iterator method that reduces the iterator's elements to a single, final value, starting from the back. Read more

Searches for an element of an iterator from the back that satisfies a predicate. Read more

impl<I: ExactSizeIterator + ?Sized> ExactSizeIterator for Box<I>
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Returns the exact number of times the iterator will iterate. Read more

🔬 This is a nightly-only experimental API. (exact_size_is_empty #35428)

Returns whether the iterator is empty. Read more

impl<I: FusedIterator + ?Sized> FusedIterator for Box<I>
1.26.0
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impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + 'a>
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The returned type after the call operator is used.

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

Performs the call operation.

impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output = R> + Send + 'a>
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The returned type after the call operator is used.

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

Performs the call operation.

impl<T: ?Sized + Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T>
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impl<T: Clone> Clone for Box<[T]>
1.3.0
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Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

impl<T: ?Sized> Borrow<T> for Box<T>
1.1.0
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Immutably borrows from an owned value. Read more

impl<T: ?Sized> BorrowMut<T> for Box<T>
1.1.0
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Mutably borrows from an owned value. Read more

impl<T: ?Sized> AsRef<T> for Box<T>
1.5.0
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Performs the conversion.

impl<T: ?Sized> AsMut<T> for Box<T>
1.5.0
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Performs the conversion.

impl<T: ?Sized> Unpin for Box<T>
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impl<T: ?Sized> Generator for Box<T> where
    T: Generator
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🔬 This is a nightly-only experimental API. (generator_trait #43122)

The type of value this generator yields. Read more

🔬 This is a nightly-only experimental API. (generator_trait #43122)

The type of value this generator returns. Read more

🔬 This is a nightly-only experimental API. (generator_trait #43122)

Resumes the execution of this generator. Read more

impl<F: ?Sized + Future + Unpin> Future for Box<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.

🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

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<'a, T, F> UnsafeFutureObj<'a, T> for Box<F> where
    F: Future<Output = T> + 'a, 
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🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

Convert an owned instance into a (conceptually owned) void pointer.

🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

Poll the future represented by the given void pointer. Read more

🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

Drops the future represented by the given void pointer. Read more

impl<Sp: ?Sized> Spawn for Box<Sp> where
    Sp: Spawn
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🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

Spawns a new task with the given future. The future will be polled until completion. Read more

🔬 This is a nightly-only experimental API. (futures_api #50547)

futures in libcore are unstable

Determines whether the executor is able to spawn new tasks. Read more

impl<'a, F: Future<Output = ()> + Send + 'a> From<Box<F>> for FutureObj<'a, ()>
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Performs the conversion.

impl<'a, F: Future<Output = ()> + 'a> From<Box<F>> for LocalFutureObj<'a, ()>
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Performs the conversion.

impl<T: Unpin + ?Sized> From<PinBox<T>> for Box<T>
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Important traits for Box<I>

Performs the conversion.

impl<T: ?Sized> From<Box<T>> for Arc<T>
1.21.0
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Performs the conversion.

impl<T: ?Sized> From<Box<T>> for Rc<T>
1.21.0
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Performs the conversion.

impl<T: ?Sized> From<Box<T>> for PinBox<T>
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Performs the conversion.

impl From<Box<str>> for String
1.18.0
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Performs the conversion.

impl From<String> for Box<str>
1.20.0
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Important traits for Box<I>

Performs the conversion.

impl<T> From<Box<[T]>> for Vec<T>
1.18.0
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Performs the conversion.

impl<T> From<Vec<T>> for Box<[T]>
1.20.0
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Important traits for Box<I>

Performs the conversion.

Auto Trait Implementations

impl<T: ?Sized> Send for Box<T> where
    T: Send

impl<T: ?Sized> Sync for Box<T> where
    T: Sync

Blanket Implementations

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

🔬 This is a nightly-only experimental API. (fnbox #28796)

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

impl<T> ToOwned for T where
    T: Clone
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Creates owned data from borrowed data, usually by cloning. Read more

🔬 This is a nightly-only experimental API. (toowned_clone_into #41263)

recently added

Uses borrowed data to replace owned data, usually by cloning. Read more

impl<T> ToString for T where
    T: Display + ?Sized
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Converts the given value to a String. Read more

impl<I> IntoIterator for I where
    I: Iterator
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The type of the elements being iterated over.

Which kind of iterator are we turning this into?

Creates an iterator from a value. Read more

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.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

impl<T> From for T
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Performs the conversion.

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.

🔬 This is a nightly-only experimental API. (try_from #33417)

Performs the conversion.

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

Performs the conversion.

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

Immutably borrows from an owned value. Read more

impl<T> BorrowMut for T where
    T: ?Sized
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Mutably borrows from an owned value. Read more

impl<T> Any for T where
    T: 'static + ?Sized
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🔬 This is a nightly-only experimental API. (get_type_id #27745)

this method will likely be replaced by an associated static

Gets the TypeId of self. Read more