Struct std::boxed::Box

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

A pointer type for heap allocation.

See the module-level documentation for more.

Methods

impl<T> Box<T>

fn new(x: T) -> Box<T>

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

Examples

let five = Box::new(5);

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

unsafe fn from_raw(raw: *mut T) -> Box<T>

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) };

fn into_raw(b: Box<T>) -> *mut T

Consumes the Box, returning the wrapped raw pointer.

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);

impl Box<Any + 'static>

fn downcast<T>(self) -> Result<Box<T>, Box<Any + 'static>> where T: Any

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 + 'static + Send>

fn downcast<T>(self) -> Result<Box<T>, Box<Any + 'static + Send>> where T: Any

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, U> CoerceUnsized<Box<U>> for Box<T> where T: Unsize<U> + ?Sized,
        U: ?Sized

impl<T> Default for Box<T> where T: Default

fn default() -> Box<T>

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

impl<T> Default for Box<[T]>

fn default() -> Box<[T]>

Returns the "default value" for a type.

impl<T> Hash for Box<T> where T: Hash + ?Sized

fn hash<H>(&self, state: &mut H) where H: Hasher

Feeds this value into the state given, updating the hasher as necessary.

fn hash_slice<H>(data: &[Self], state: &mut H) where H: Hasher

Feeds a slice of this type into the state provided.

impl<T> PartialEq<Box<T>> for Box<T> where T: PartialEq<T> + ?Sized

fn eq(&self, other: &Box<T>) -> bool

This method tests for self and other values to be equal, and is used by ==.

fn ne(&self, other: &Box<T>) -> bool

This method tests for !=.

impl<I> ExactSizeIterator for Box<I> where I: ExactSizeIterator + ?Sized

fn len(&self) -> usize

Returns the exact number of times the iterator will iterate.

fn is_empty(&self) -> bool

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

Returns whether the iterator is empty.

impl<T> PartialOrd<Box<T>> for Box<T> where T: PartialOrd<T> + ?Sized

fn partial_cmp(&self, other: &Box<T>) -> Option<Ordering>

This method returns an ordering between self and other values if one exists.

fn lt(&self, other: &Box<T>) -> bool

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

fn le(&self, other: &Box<T>) -> bool

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

fn ge(&self, other: &Box<T>) -> bool

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

fn gt(&self, other: &Box<T>) -> bool

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

impl<I> Iterator for Box<I> where I: Iterator + ?Sized

type Item = I::Item

The type of the elements being iterated over.

fn next(&mut self) -> Option<I::Item>

Advances the iterator and returns the next value.

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

Returns the bounds on the remaining length of the iterator.

fn nth(&mut self, n: usize) -> Option<I::Item>

Returns the nth element of the iterator.

fn count(self) -> usize

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

fn last(self) -> Option<Self::Item>

Consumes the iterator, returning the last element.

fn chain<U>(self, other: U) -> Chain<Self, U::IntoIter> where U: IntoIterator<Item=Self::Item>

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

fn zip<U>(self, other: U) -> Zip<Self, U::IntoIter> where U: IntoIterator

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

fn map<B, F>(self, f: F) -> Map<Self, F> where F: FnMut(Self::Item) -> B

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

fn filter<P>(self, predicate: P) -> Filter<Self, P> where P: FnMut(&Self::Item) -> bool

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

fn filter_map<B, F>(self, f: F) -> FilterMap<Self, F> where F: FnMut(Self::Item) -> Option<B>

Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>

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

fn peekable(self) -> Peekable<Self>

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

fn skip_while<P>(self, predicate: P) -> SkipWhile<Self, P> where P: FnMut(&Self::Item) -> bool

Creates an iterator that [skip()]s elements based on a predicate.

fn take_while<P>(self, predicate: P) -> TakeWhile<Self, P> where P: FnMut(&Self::Item) -> bool

Creates an iterator that yields elements based on a predicate.

fn skip(self, n: usize) -> Skip<Self>

Creates an iterator that skips the first n elements.

fn take(self, n: usize) -> Take<Self>

Creates an iterator that yields its first n elements.

fn scan<St, B, F>(self, initial_state: St, f: F) -> Scan<Self, St, F> where F: FnMut(&mut St, Self::Item) -> Option<B>

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

fn flat_map<U, F>(self, f: F) -> FlatMap<Self, U, F> where F: FnMut(Self::Item) -> U, U: IntoIterator

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

fn fuse(self) -> Fuse<Self>

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

fn inspect<F>(self, f: F) -> Inspect<Self, F> where F: FnMut(&Self::Item) -> ()

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

fn by_ref(&mut self) -> &mut Self

Borrows an iterator, rather than consuming it.

fn collect<B>(self) -> B where B: FromIterator<Self::Item>

Transforms an iterator into a collection.

fn partition<B, F>(self, f: F) -> (B, B) where B: Default + Extend<Self::Item>, F: FnMut(&Self::Item) -> bool

Consumes an iterator, creating two collections from it.

fn fold<B, F>(self, init: B, f: F) -> B where F: FnMut(B, Self::Item) -> B

An iterator adaptor that applies a function, producing a single, final value.

fn all<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool

Tests if every element of the iterator matches a predicate.

fn any<F>(&mut self, f: F) -> bool where F: FnMut(Self::Item) -> bool

Tests if any element of the iterator matches a predicate.

fn find<P>(&mut self, predicate: P) -> Option<Self::Item> where P: FnMut(&Self::Item) -> bool

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

fn position<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool

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

fn rposition<P>(&mut self, predicate: P) -> Option<usize> where P: FnMut(Self::Item) -> bool,
        Self: ExactSizeIterator + DoubleEndedIterator

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

fn max(self) -> Option<Self::Item> where Self::Item: Ord

Returns the maximum element of an iterator.

fn min(self) -> Option<Self::Item> where Self::Item: Ord

Returns the minimum element of an iterator.

fn max_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B

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

fn max_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering

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

fn min_by_key<B, F>(self, f: F) -> Option<Self::Item> where B: Ord, F: FnMut(&Self::Item) -> B

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

fn min_by<F>(self, compare: F) -> Option<Self::Item> where F: FnMut(&Self::Item, &Self::Item) -> Ordering

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

fn rev(self) -> Rev<Self> where Self: DoubleEndedIterator

Reverses an iterator's direction.

fn unzip<A, B, FromA, FromB>(self) -> (FromA, FromB) where FromA: Default + Extend<A>,
        FromB: Default + Extend<B>,
        Self: Iterator<Item=(A, B)>

Converts an iterator of pairs into a pair of containers.

fn cloned<'a, T>(self) -> Cloned<Self> where Self: Iterator<Item=&'a T>, T: 'a + Clone

Creates an iterator which [clone()]s all of its elements.

fn cycle(self) -> Cycle<Self> where Self: Clone

Repeats an iterator endlessly.

fn sum<S>(self) -> S where S: Sum<Self::Item>

Sums the elements of an iterator.

fn product<P>(self) -> P where P: Product<Self::Item>

Iterates over the entire iterator, multiplying all the elements

fn cmp<I>(self, other: I) -> Ordering where I: IntoIterator<Item=Self::Item>, Self::Item: Ord

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

fn partial_cmp<I>(self, other: I) -> Option<Ordering> where I: IntoIterator, Self::Item: PartialOrd<I::Item>

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

fn eq<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>

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

fn ne<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialEq<I::Item>

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

fn lt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>

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

fn le<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>

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

fn gt<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>

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

fn ge<I>(self, other: I) -> bool where I: IntoIterator, Self::Item: PartialOrd<I::Item>

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

impl<T> From<T> for Box<T>

fn from(t: T) -> Box<T>

Performs the conversion.

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

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

Formats the value using the given formatter.

impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output=R> + 'a>

type Output = R

The returned type after the call operator is used.

extern "rust-call" fn call_once(self, args: A) -> R

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

This is called when the call operator is used.

impl<'a, A, R> FnOnce<A> for Box<FnBox<A, Output=R> + 'a + Send>

type Output = R

The returned type after the call operator is used.

extern "rust-call" fn call_once(self, args: A) -> R

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

This is called when the call operator is used.

impl<I> FusedIterator for Box<I> where I: FusedIterator + ?Sized

impl<T> Clone for Box<T> where T: Clone

fn clone(&self) -> Box<T>

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

Examples

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

fn clone_from(&mut self, source: &Box<T>)

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>

fn clone(&self) -> Box<str>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl<T> Clone for Box<[T]> where T: Clone

fn clone(&self) -> Box<[T]>

Returns a copy of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

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

type Target = T

The resulting type after dereferencing

fn deref(&self) -> &T

The method called to dereference a value

impl<T> Boxed for Box<T>

type Data = T

🔬 This is a nightly-only experimental API.   (placement_new_protocol)

The kind of data that is stored in this kind of box.

type Place = IntermediateBox<T>

🔬 This is a nightly-only experimental API.   (placement_new_protocol)

The place that will negotiate the storage of the data.

unsafe fn finalize(b: IntermediateBox<T>) -> Box<T>

🔬 This is a nightly-only experimental API.   (placement_new_protocol)

Converts filled place into final owning value, shifting deallocation/cleanup responsibilities (if any remain), over to returned instance of Self and forgetting filled.

impl<T> Eq for Box<T> where T: Eq + ?Sized

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

fn as_ref(&self) -> &T

Performs the conversion.

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

fn borrow(&self) -> &T

Immutably borrows from an owned value.

impl<T> Debug for Box<T> where T: Debug + ?Sized

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

Formats the value using the given formatter.

impl<T> Ord for Box<T> where T: Ord + ?Sized

fn cmp(&self, other: &Box<T>) -> Ordering

This method returns an Ordering between self and other.

impl<T> Display for Box<T> where T: Display + ?Sized

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

Formats the value using the given formatter.

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

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

The method called to mutably dereference a value

impl<I> DoubleEndedIterator for Box<I> where I: DoubleEndedIterator + ?Sized

fn next_back(&mut self) -> Option<I::Item>

Removes and returns an element from the end of the iterator.

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

fn as_mut(&mut self) -> &mut T

Performs the conversion.

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

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

Mutably borrows from an owned value.

impl<'a, E: Error + 'a> From<E> for Box<Error + 'a>

fn from(err: E) -> Box<Error + 'a>

Performs the conversion.

impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<Error + Send + Sync + 'a>

fn from(err: E) -> Box<Error + Send + Sync + 'a>

Performs the conversion.

impl From<String> for Box<Error + Send + Sync>

fn from(err: String) -> Box<Error + Send + Sync>

Performs the conversion.

impl From<String> for Box<Error>

fn from(str_err: String) -> Box<Error>

Performs the conversion.

impl<'a, 'b> From<&'b str> for Box<Error + Send + Sync + 'a>

fn from(err: &'b str) -> Box<Error + Send + Sync + 'a>

Performs the conversion.

impl<'a> From<&'a str> for Box<Error>

fn from(err: &'a str) -> Box<Error>

Performs the conversion.

impl<T: Error> Error for Box<T>

fn description(&self) -> &str

A short description of the error.

fn cause(&self) -> Option<&Error>

The lower-level cause of this error, if any.