collections::boxed::Box

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);

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 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);

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));
}

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));
}

Performs the conversion.

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

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

Immutably borrows from an owned value. Read more

Formats the value using the given formatter.

Returns the exact number of times the iterator will iterate. Read more

Returns whether the iterator is empty. Read more

Formats the value using the given formatter.

Mutably borrows from an owned value. Read more

This method returns an Ordering between self and other. Read more

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

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

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

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

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

Creates an iterator that both filters and maps. Read more

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

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

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

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

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

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

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

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

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

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 adaptor 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

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

Reverses an iterator's direction. Read more

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

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

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

The returned type after the call operator is used.

This is called when the call operator is used.

The returned type after the call operator is used.

This is called when the call operator is used.

Formats the value using the given formatter. Read more

Performs the conversion.

Performs the conversion.

Performs the conversion.

A method called when the value goes out of scope. Read more

The method called to mutably dereference a value

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);

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

Returns a copy of the value. Read more

Performs copy-assignment from source. Read more

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

Feeds this value into the given [Hasher]. Read more

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

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

This method tests for !=.

The resulting type after dereferencing

The method called to dereference a value

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

The place that will negotiate the storage of the data.

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

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

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

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

Performs the conversion.