Struct bumpalo::boxed::Box

source · 
#[repr(transparent)]
pub struct Box<'a, T: ?Sized>(_);
Expand description

An owned pointer to a bump-allocated T value, that runs Drop implementations.

See the module-level documentation for more details.

Implementations§

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

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

Examples
use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let five = Box::new_in(5, &b);

Constructs a new Pin<Box<T>>. If T does not implement Unpin, then x will be pinned in memory and unable to be moved.

Consumes the Box, returning the wrapped value.

Examples
use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let hello = Box::new_in("hello".to_owned(), &b);
assert_eq!(Box::into_inner(hello), "hello");

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. For this to be safe, the memory must have been allocated in accordance with the memory layout used by Box .

Safety

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

Recreate a Box which was previously converted to a raw pointer using Box::into_raw:

use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let x = Box::new_in(5, &b);
let ptr = Box::into_raw(x);
let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.

Manually create a Box from scratch by using the bump allocator:

use std::alloc::{alloc, Layout};
use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

unsafe {
    let ptr = b.alloc_layout(Layout::new::<i32>()).as_ptr() as *mut i32;
    *ptr = 5;
    let x = Box::from_raw(ptr); // Note that `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.
}

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 value previously managed by the Box. In particular, the caller should properly destroy T. The easiest way to do this is to convert the raw pointer back into a Box with the Box::from_raw function, allowing the Box destructor to perform the cleanup.

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

Converting the raw pointer back into a Box with Box::from_raw for automatic cleanup:

use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let x = Box::new_in(String::from("Hello"), &b);
let ptr = Box::into_raw(x);
let x = unsafe { Box::from_raw(ptr) }; // Note that new `x`'s lifetime is unbound. It must be bound to the `b` immutable borrow before `b` is reset.

Manual cleanup by explicitly running the destructor:

use std::ptr;
use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let mut x = Box::new_in(String::from("Hello"), &b);
let p = Box::into_raw(x);
unsafe {
    ptr::drop_in_place(p);
}

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:

use bumpalo::{Bump, boxed::Box};

let b = Bump::new();

let x = Box::new_in(41, &b);
let reference: &mut usize = Box::leak(x);
*reference += 1;
assert_eq!(*reference, 42);
 use bumpalo::{Bump, boxed::Box, vec};

 let b = Bump::new();

 let x = vec![in &b; 1, 2, 3].into_boxed_slice();
 let reference = Box::leak(x);
 reference[0] = 4;
 assert_eq!(*reference, [4, 2, 3]);

Attempt to downcast the box to a concrete type.

Examples
use std::any::Any;

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

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

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

Creates a value from an iterator. This method is an adapted version of FromIterator::from_iter. It cannot be made as that trait implementation given different signature.

Examples

Basic usage:

use bumpalo::{Bump, boxed::Box, vec};

let b = Bump::new();

let five_fives = std::iter::repeat(5).take(5);
let slice = Box::from_iter_in(five_fives, &b);
assert_eq!(vec![in &b; 5, 5, 5, 5, 5], &*slice);

Trait Implementations§

Converts this type into a mutable reference of the (usually inferred) input type.
Converts this type into a shared reference of the (usually inferred) input type.
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more
Formats the value using the given formatter. Read more
Returns the “default value” for a type. Read more
Returns the “default value” for a type. Read more
The resulting type after dereferencing.
Dereferences the value.
Mutably dereferences the value.
Formats the value using the given formatter. Read more
Removes and returns an element from the end of the iterator. Read more
Returns the nth element from the end of the iterator. Read more
🔬This is a nightly-only experimental API. (iter_advance_by)
Advances the iterator from the back by n elements. Read more
This is the reverse version of Iterator::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
Executes the destructor for this type. Read more
Returns the exact remaining length of the iterator. Read more
🔬This is a nightly-only experimental API. (exact_size_is_empty)
Returns true if the iterator is empty. Read more

This impl replaces unsize coercion.

Converts to this type from the input type.

Converts a Box<T> into a Pin<Box<T>>.

This conversion does not allocate on the heap and happens in place.

Converts to this type from the input type.
The allocator type
Similar to FromIterator::from_iter, but with a given allocator. Read more
The type of value produced on completion.
Attempt to resolve the future to a final value, registering the current task for wakeup if the value is not yet available. Read more
Feeds this value into the given Hasher. Read more
Feeds a slice of this type into the given Hasher. Read more
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.
🔬This is a nightly-only experimental API. (hasher_prefixfree_extras)
Writes a length prefix into this hasher, as part of being prefix-free. Read more
🔬This is a nightly-only experimental API. (hasher_prefixfree_extras)
Writes a single str into this hasher. 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, returning the last element. Read more
🔬This is a nightly-only experimental API. (iter_next_chunk)
Advances the iterator and returns an array containing the next N values. Read more
Consumes the iterator, counting the number of iterations and returning it. Read more
🔬This is a nightly-only experimental API. (iter_advance_by)
Advances the iterator by n elements. Read more
Creates an iterator starting at the same point, but stepping by the given amount at each iteration. 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
🔬This is a nightly-only experimental API. (iter_intersperse)
Creates a new iterator which places an item generated by separator between adjacent items of the original iterator. Read more
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
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 the peek and peek_mut methods to look at the next element of the iterator without consuming it. See their documentation for more information. Read more
Creates an iterator that skips elements based on a predicate. Read more
Creates an iterator that yields elements based on a predicate. Read more
Creates an iterator that both yields elements based on a predicate and maps. Read more
Creates an iterator that skips the first n elements. Read more
Creates an iterator that yields the first n elements, or fewer if the underlying iterator ends sooner. Read more
An iterator adapter which, like fold, holds internal state, but unlike fold, 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
Does 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
🔬This is a nightly-only experimental API. (iter_collect_into)
Collects all the items from an iterator into a collection. Read more
Consumes an iterator, creating two collections from it. Read more
🔬This is a nightly-only experimental API. (iter_is_partitioned)
Checks if the elements of this iterator are partitioned according to the given predicate, such that all those that return true precede all those that return false. 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
Folds every element into an accumulator by applying an operation, returning the final result. Read more
Reduces the elements to a single one, by repeatedly applying a reducing operation. Read more
🔬This is a nightly-only experimental API. (iterator_try_reduce)
Reduces the elements to a single one by repeatedly applying a reducing operation. If the closure returns a failure, the failure is propagated back to the caller immediately. 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
🔬This is a nightly-only experimental API. (try_find)
Applies function to the elements of iterator and returns the first true result or the first error. Read more
Searches for an element in an iterator, returning its index. 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
Converts an iterator of pairs into a pair of containers. Read more
Creates an iterator which copies all of its elements. Read more
Creates an iterator which clones all of its elements. Read more
🔬This is a nightly-only experimental API. (iter_array_chunks)
Returns an iterator over N elements of the iterator at a time. Read more
Sums the elements of an iterator. Read more
Iterates over the entire iterator, multiplying all the elements Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
Lexicographically compares the elements of this Iterator with those of another. Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Lexicographically compares the elements of this Iterator with those of another with respect to the specified comparison function. Read more
Determines if the elements of this Iterator are equal to those of another. Read more
🔬This is a nightly-only experimental API. (iter_order_by)
Determines if the elements of this Iterator are equal to those of another with respect to the specified equality function. 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
🔬This is a nightly-only experimental API. (is_sorted)
Checks if the elements of this iterator are sorted using the given comparator function. Read more
🔬This is a nightly-only experimental API. (is_sorted)
Checks if the elements of this iterator are sorted using the given key extraction function. Read more
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
Restrict a value to a certain interval. Read more
This method tests for self and other values to be equal, and is used by ==.
This method tests for !=. The default implementation is almost always sufficient, and should not be overridden without very good reason.
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
Formats the value using the given formatter.

This impl replaces unsize coercion.

The type returned in the event of a conversion error.
Performs the conversion.

Auto Trait Implementations§

Blanket Implementations§

Gets the TypeId of self. Read more
Immutably borrows from an owned value. Read more
Mutably borrows from an owned value. Read more

Returns the argument unchanged.

Calls U::from(self).

That is, this conversion is whatever the implementation of From<T> for U chooses to do.

The output that the future will produce on completion.
Which kind of future are we turning this into?
Creates a future from a value. Read more
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
Converts the given value to a String. Read more
The type returned in the event of a conversion error.
Performs the conversion.
The type returned in the event of a conversion error.
Performs the conversion.