Struct alloc::boxed::Box

[+] Show declaration

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

[−] Expand description

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>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

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

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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);

pub fn pinned(x: T) -> Pin<Box<T>>

🔬 This is a nightly-only experimental API. (pin #49150)

impl<T: ?Sized> Box<T>

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pub unsafe fn from_raw(raw: *mut T) -> Self

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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) };

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

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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);

pub fn into_raw_non_null(b: Box<T>) -> NonNull<T>

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🔬 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);
}

pub fn leak<'a>(b: Box<T>) -> &'a mut T where     T: 'a,

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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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pub fn downcast<T: Any>(self) -> Result<Box<T>, 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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pub fn downcast<T: Any>(self) -> Result<Box<T>, 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 + PartialEq> PartialEq<Box<T>> for Box<T>

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

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

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

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This method tests for !=.

impl<T: ?Sized + Eq> Eq for Box<T>

impl<T: ?Sized + Ord> Ord for Box<T>

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

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This method returns an Ordering between self and other.

fn max(self, other: Self) -> Self

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Compares and returns the maximum of two values.

fn min(self, other: Self) -> Self

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Compares and returns the minimum of two values.

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

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

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

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

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

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

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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

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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

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

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

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

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

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Formats the value using the given formatter.

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

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

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Formats the value using the given formatter.

impl<T: ?Sized> Deref for Box<T>

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type Target = T

The resulting type after dereferencing.

fn deref(&self) -> &T

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Dereferences the value.

impl<T: ?Sized> DerefMut for Box<T>

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

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Mutably dereferences the value.

impl<T: ?Sized> Drop for Box<T>

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fn drop(&mut self)

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Executes the destructor for this type.

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

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type Output = R

The returned type after the call operator is used.

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

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🔬 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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type Output = R

The returned type after the call operator is used.

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

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

Performs the call operation.

impl<T: ?Sized> Generator for Box<T> where     T: Generator,

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type Yield = T::Yield

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

The type of value this generator yields.

type Return = T::Return

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

The type of value this generator returns.

unsafe fn resume(&mut self) -> GeneratorState<Self::Yield, Self::Return>

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

Resumes the execution of this generator.

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

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

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Feeds this value into the given [Hasher].

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

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

impl<T: ?Sized + Hasher> Hasher for Box<T>

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fn finish(&self) -> u64

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Returns the hash value for the values written so far.

fn write(&mut self, bytes: &[u8])

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Writes some data into this Hasher.

fn write_u8(&mut self, i: u8)

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Writes a single u8 into this hasher.

fn write_u16(&mut self, i: u16)

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Writes a single u16 into this hasher.

fn write_u32(&mut self, i: u32)

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Writes a single u32 into this hasher.

fn write_u64(&mut self, i: u64)

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Writes a single u64 into this hasher.

fn write_u128(&mut self, i: u128)

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Writes a single u128 into this hasher.

fn write_usize(&mut self, i: usize)

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Writes a single usize into this hasher.

fn write_i8(&mut self, i: i8)

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Writes a single i8 into this hasher.

fn write_i16(&mut self, i: i16)

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Writes a single i16 into this hasher.

fn write_i32(&mut self, i: i32)

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Writes a single i32 into this hasher.

fn write_i64(&mut self, i: i64)

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Writes a single i64 into this hasher.

fn write_i128(&mut self, i: i128)

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Writes a single i128 into this hasher.

fn write_isize(&mut self, i: isize)

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Writes a single isize into this hasher.

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

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

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type Item = I::Item

The type of the elements being iterated over.

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

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Advances the iterator and returns the next value.

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

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Returns the bounds on the remaining length of the iterator.

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

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Returns the nth element of the iterator.

fn count(self) -> usize

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

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

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Consumes the iterator, returning the last element.

fn step_by(self, step: usize) -> StepBy<Self>

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

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

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

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

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'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,

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

fn for_each<F>(self, f: F) where     F: FnMut(Self::Item),

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Calls a closure on each element of an iterator.

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

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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>,

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Creates an iterator that both filters and maps.

fn enumerate(self) -> Enumerate<Self>

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

fn peekable(self) -> Peekable<Self>

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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,

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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,

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Creates an iterator that yields elements based on a predicate.

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

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Creates an iterator that skips the first n elements.

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

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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>,

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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,

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

fn flatten(self) -> Flatten<Self> where     Self::Item: IntoIterator,

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Creates an iterator that flattens nested structure.

fn fuse(self) -> Fuse<Self>

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

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

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

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

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Borrows an iterator, rather than consuming it.

[+] Expand attributes #[must_use = "if you really need to exhaust the iterator, consider `.for_each(drop)` instead"] fn collect<B>(self) -> B where     B: FromIterator<Self::Item>,

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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,

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Consumes an iterator, creating two collections from it.

fn try_fold<B, F, R>(&mut self, init: B, f: F) -> R where     F: FnMut(B, Self::Item) -> R,     R: Try<Ok = B>,

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

fn try_for_each<F, R>(&mut self, f: F) -> R where     F: FnMut(Self::Item) -> R,     R: Try<Ok = ()>,

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

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

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

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

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Tests if every element of the iterator matches a predicate.

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

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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,

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

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

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

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

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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,

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

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

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Returns the maximum element of an iterator.

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

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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,

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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,

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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,

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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,

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

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

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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)>,

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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,

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

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

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Repeats an iterator endlessly.

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

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Sums the elements of an iterator.

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

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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,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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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 as IntoIterator>::Item>,

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

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

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

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

fn try_rfold<B, F, R>(&mut self, init: B, f: F) -> R where     F: FnMut(B, Self::Item) -> R,     R: Try<Ok = B>,

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

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

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

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

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

impl<T: ?Sized> Unpin for Box<T>

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

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fn len(&self) -> usize

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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 #35428)

Returns whether the iterator is empty.

impl<T: ?Sized> Pointer for Box<T>

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

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Formats the value using the given formatter.

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

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fn from(t: T) -> Self

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Performs the conversion.

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

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fn from(boxed: Box<T>) -> Self

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Performs the conversion.

impl<'a, T: Copy> From<&'a [T]> for Box<[T]>

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Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn from(slice: &'a [T]) -> Box<[T]>

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Performs the conversion.

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

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Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

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

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Performs the conversion.

impl From<Box<str>> for Box<[u8]>

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fn from(s: Box<str>) -> Self

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Performs the conversion.

impl<T: ?Sized> From<Box<T>> for Arc<T>

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fn from(v: Box<T>) -> Arc<T>

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Performs the conversion.

impl<T: ?Sized> From<Box<T>> for Rc<T>

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fn from(v: Box<T>) -> Rc<T>

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Performs the conversion.

impl From<Box<str>> for String

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fn from(s: Box<str>) -> String

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Performs the conversion.

impl From<String> for Box<str>

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Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn from(s: String) -> Box<str>

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Performs the conversion.

impl<T> From<Box<[T]>> for Vec<T>

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fn from(s: Box<[T]>) -> Vec<T>

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Performs the conversion.

impl<T> From<Vec<T>> for Box<[T]>

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Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn from(v: Vec<T>) -> Box<[T]>

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Performs the conversion.

impl<T: Clone> Clone for Box<T>

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Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

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

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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>)

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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>

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fn clone(&self) -> Self

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Returns a copy of the value.

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

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Performs copy-assignment from source.

impl<T: Clone> Clone for Box<[T]>

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fn clone(&self) -> Self

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Returns a copy of the value.

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

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Performs copy-assignment from source.

impl<T: ?Sized> AsRef<T> for Box<T>

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fn as_ref(&self) -> &T

[−]

Performs the conversion.

impl<T: Default> Default for Box<T>

[+]

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn default() -> Box<T>

[−]

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

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

[+]

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

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

[−]

Returns the "default value" for a type.

impl Default for Box<str>

[+]

Important traits for Box<I>

impl<I: Iterator + ?Sized> Iterator for Box<I> type Item = I::Item;

fn default() -> Box<str>

[−]

Returns the "default value" for a type.

impl<T: ?Sized> AsMut<T> for Box<T>

[+]

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

[−]

Performs the conversion.

impl<T: ?Sized> Borrow<T> for Box<T>

[+]

fn borrow(&self) -> &T

[−]

Immutably borrows from an owned value.

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

[+]

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

[−]

Mutably borrows from an owned value.

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

[+]

type Output = F::Output

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

futures in libcore are unstable

The result of the Future.

fn poll(self: Pin<&mut Self>, lw: &LocalWaker) -> Poll<Self::Output>

[−]

🔬 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.