1.0.0[][src]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>
[src]

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);Run

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

impl<T> Box<T> where
    T: ?Sized
[src]

Important traits for Box<I>

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) };Run

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);Run

🔬 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);
}Run

Important traits for &'_ mut I

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);
}Run

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]);
}Run

impl Box<dyn Any + 'static>
[src]

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));
}Run

impl Box<dyn Any + 'static + Send>
[src]

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));
}Run

Trait Implementations

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

impl Clone for Box<str>
1.3.0
[src]

Performs copy-assignment from source. Read more

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

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();Run

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);Run

impl<T> Clone for Box<[T]> where
    T: Clone
1.3.0
[src]

Performs copy-assignment from source. Read more

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

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

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> Iterator for Box<I> where
    I: Iterator + ?Sized
[src]

The type of the elements being iterated over.

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

Important traits for &'_ mut I

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<T> Ord for Box<T> where
    T: Ord + ?Sized
[src]

Compares and returns the maximum of two values. Read more

Compares and returns the minimum of two values. Read more

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

impl<T> Generator for Box<T> where
    T: Generator + ?Sized
[src]

🔬 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

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

The resulting type after dereferencing.

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

impl<T> Default for Box<T> where
    T: Default
[src]

Important traits for Box<I>

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

impl Default for Box<str>
1.17.0
[src]

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

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

The returned type after the call operator is used.

impl<'a, A, R> FnOnce<A> for Box<dyn FnBox<A, Output = R> + 'a>
[src]

The returned type after the call operator is used.

impl<T> AsMut<T> for Box<T> where
    T: ?Sized
1.5.0
[src]

impl<A> FromIterator<A> for Box<[A]>
1.32.0
[src]

impl<T, U> DispatchFromDyn<Box<U>> for Box<T> where
    T: Unsize<U> + ?Sized,
    U: ?Sized
[src]

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

impl<F> Future for Box<F> where
    F: Unpin + Future + ?Sized
[src]

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

futures in libcore are unstable

The result of the Future.

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

impl<I> FusedIterator for Box<I> where
    I: FusedIterator + ?Sized
1.26.0
[src]

impl<T> Borrow<T> for Box<T> where
    T: ?Sized
1.1.0
[src]

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

impl<T> BorrowMut<T> for Box<T> where
    T: ?Sized
1.1.0
[src]

impl<T> AsRef<T> for Box<T> where
    T: ?Sized
1.5.0
[src]

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

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

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

impl<T> From<Box<[T]>> for Vec<T>
1.18.0
[src]

impl<T> From<Box<T>> for Arc<T> where
    T: ?Sized
1.21.0
[src]

impl<'a> From<&'a str> for Box<str>
1.17.0
[src]

impl<T> From<T> for Box<T>
1.6.0
[src]

impl From<Box<str>> for String
1.18.0
[src]

Converts the given boxed str slice to a String. It is notable that the str slice is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2: Box<str> = s1.into_boxed_str();
let s3: String = String::from(s2);

assert_eq!("hello world", s3)Run

impl<'a, T> From<&'a [T]> for Box<[T]> where
    T: Copy
1.17.0
[src]

impl<T> From<Vec<T>> for Box<[T]>
1.20.0
[src]

impl From<String> for Box<str>
1.20.0
[src]

Important traits for Box<I>

Converts the given String to a boxed str slice that is owned.

Examples

Basic usage:

let s1: String = String::from("hello world");
let s2: Box<str> = Box::from(s1);
let s3: String = String::from(s2);

assert_eq!("hello world", s3)Run

impl From<Box<str>> for Box<[u8]>
1.19.0
[src]

impl<T> From<Box<T>> for Pin<Box<T>>
[src]

impl<T> From<Box<T>> for Rc<T> where
    T: ?Sized
1.21.0
[src]

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

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

impl<T, U> CoerceUnsized<Box<U>> for Box<T> where
    T: Unsize<U> + ?Sized,
    U: ?Sized
[src]

impl<T> Hasher for Box<T> where
    T: Hasher + ?Sized
1.22.0
[src]

impl<T: Error> Error for Box<T>
1.8.0
[src]

The lower-level source of this error, if any. Read more

impl<R: Read + ?Sized> Read for Box<R>
[src]

Important traits for &'_ mut I

Creates a "by reference" adaptor for this instance of Read. Read more

Important traits for Bytes<R>

Transforms this Read instance to an [Iterator] over its bytes. Read more

Important traits for Chain<T, U>

Creates an adaptor which will chain this stream with another. Read more

Important traits for Take<T>

Creates an adaptor which will read at most limit bytes from it. Read more

impl<W: Write + ?Sized> Write for Box<W>
[src]

Important traits for &'_ mut I

Creates a "by reference" adaptor for this instance of Write. Read more

impl<S: Seek + ?Sized> Seek for Box<S>
[src]

impl<B: BufRead + ?Sized> BufRead for Box<B>
[src]

Important traits for Split<B>

Returns an iterator over the contents of this reader split on the byte byte. Read more

Important traits for Lines<B>

Returns an iterator over the lines of this reader. Read more

impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a>
[src]

Important traits for Box<I>

Converts a type of Error into a box of dyn Error.

Examples

use std::error::Error;
use std::fmt;
use std::mem;

#[derive(Debug)]
struct AnError;

impl fmt::Display for AnError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f , "An error")
    }
}

impl Error for AnError {
    fn description(&self) -> &str {
        "Description of an error"
    }
}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<Error>::from(an_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Run

impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a>
[src]

Important traits for Box<I>

Converts a type of Error + Send + Sync into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::fmt;
use std::mem;

#[derive(Debug)]
struct AnError;

impl fmt::Display for AnError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f , "An error")
    }
}

impl Error for AnError {
    fn description(&self) -> &str {
        "Description of an error"
    }
}

unsafe impl Send for AnError {}

unsafe impl Sync for AnError {}

let an_error = AnError;
assert!(0 == mem::size_of_val(&an_error));
let a_boxed_error = Box::<Error + Send + Sync>::from(an_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Run

impl From<String> for Box<dyn Error + Send + Sync>
[src]

Important traits for Box<I>

Converts a String into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<Error + Send + Sync>::from(a_string_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Run

impl From<String> for Box<dyn Error>
1.6.0
[src]

Important traits for Box<I>

Converts a String into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;

let a_string_error = "a string error".to_string();
let a_boxed_error = Box::<Error>::from(a_string_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Run

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

Important traits for Box<I>

Converts a str into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<Error + Send + Sync>::from(a_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Run

impl<'a> From<&'a str> for Box<dyn Error>
1.6.0
[src]

Important traits for Box<I>

Converts a str into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;

let a_str_error = "a str error";
let a_boxed_error = Box::<Error>::from(a_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Run

impl<'a, 'b> From<Cow<'b, str>> for Box<dyn Error + Send + Sync + 'a>
1.22.0
[src]

Important traits for Box<I>

Converts a Cow into a box of dyn Error + Send + Sync.

Examples

use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<Error + Send + Sync>::from(a_cow_str_error);
assert!(
    mem::size_of::<Box<dyn Error + Send + Sync>>() == mem::size_of_val(&a_boxed_error))Run

impl<'a> From<Cow<'a, str>> for Box<dyn Error>
1.22.0
[src]

Important traits for Box<I>

Converts a Cow into a box of dyn Error.

Examples

use std::error::Error;
use std::mem;
use std::borrow::Cow;

let a_cow_str_error = Cow::from("a str error");
let a_boxed_error = Box::<Error>::from(a_cow_str_error);
assert!(mem::size_of::<Box<dyn Error>>() == mem::size_of_val(&a_boxed_error))Run

impl<'a> From<&'a CStr> for Box<CStr>
1.17.0
[src]

impl From<Box<CStr>> for CString
1.18.0
[src]

Converts a Box<CStr> into a CString without copying or allocating.

impl From<CString> for Box<CStr>
1.20.0
[src]

Important traits for Box<I>

Converts a CString into a Box<CStr> without copying or allocating.

impl<'a> From<&'a OsStr> for Box<OsStr>
1.17.0
[src]

impl From<Box<OsStr>> for OsString
1.18.0
[src]

Converts a Box<OsStr> into a OsString without copying or allocating.

impl From<OsString> for Box<OsStr>
1.20.0
[src]

Important traits for Box<I>

Converts a OsString into a Box<OsStr> without copying or allocating.

impl<'a> From<&'a Path> for Box<Path>
1.17.0
[src]

impl From<Box<Path>> for PathBuf
1.18.0
[src]

impl From<PathBuf> for Box<Path>
1.20.0
[src]

impl Clone for Box<CStr>
1.29.0
[src]

Performs copy-assignment from source. Read more

impl Clone for Box<OsStr>
1.29.0
[src]

Performs copy-assignment from source. Read more

impl Clone for Box<Path>
1.29.0
[src]

Performs copy-assignment from source. Read more

impl Default for Box<CStr>
1.17.0
[src]

impl Default for Box<OsStr>
1.17.0
[src]

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

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

The type returned in the event of a conversion error.

impl<I> IntoIterator for I where
    I: Iterator
[src]

The type of the elements being iterated over.

Which kind of iterator are we turning this into?

impl<T> From for T
[src]

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

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

The type returned in the event of a conversion error.

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

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

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

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

impl<A, F> FnBox for F where
    F: FnOnce<A>, 
[src]

🔬 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
[src]

impl<T> ToString for T where
    T: Display + ?Sized
[src]