Struct Scope 

pub struct Scope<'a, B: FixedRange> { /* private fields */ }

A scratch scope over a BumpArena, created by BumpArena::scope.

Allocate through it; when it drops (normally or on a panic unwind) the arena’s cursor rewinds to where the scope began, reclaiming everything the scope allocated. References handed out by the scope borrow it (&self), so the borrow checker forbids them from outliving the rewind — no unsafe lifetime branding is needed, and a misuse is a compile error (see the compile_fail example on BumpArena::scope).

Scopes nest: call scope on a Scope to checkpoint again.

While the scope is alive the underlying arena is mutably borrowed, so it cannot be used directly — which is exactly what prevents an outer allocation from landing in the region the scope will reclaim.

Implementations

impl<'a, B: FixedRange> Scope<'a, B>

pub fn alloc_uninit<T>(&self) -> Result<&mut MaybeUninit<T>, AllocError>

Typed scratch allocation bound to this scope — see BumpArena::alloc_uninit. The returned reference borrows the scope, so it cannot outlive the rewind. Returns &mut MaybeUninit<T>; write a T before assuming it initialized.

&mut from &self is the bump-allocator idiom (cf. bumpalo::Bump::alloc): each call returns a disjoint fresh region, so the &muts never alias.

pub fn allocate(&self, layout: NonZeroLayout) -> Result<&mut [u8], AllocError>

Raw byte scratch allocation bound to this scope — see Allocator::allocate. The returned slice borrows the scope.

&mut from &self is intentional (see alloc_uninit): each call returns a disjoint fresh region.

pub fn alloc<T>(&self, value: T) -> Result<&mut T, AllocError>

Allocate and initialize one T as scratch, bound to this scope — see BumpArena::alloc. The returned &mut T cannot outlive the rewind.

pub fn alloc_slice_copy<T: Copy>( &self, src: &[T], ) -> Result<&mut [T], AllocError>

Copy a slice into the scope, bound to it — see BumpArena::alloc_slice_copy. The returned &mut [T] cannot outlive the rewind.

pub fn alloc_str(&self, s: &str) -> Result<&mut str, AllocError>

Copy a string into the scope, bound to it — see BumpArena::alloc_str. The returned &mut str cannot outlive the rewind.

pub fn arena_allocated(&self) -> usize

Bytes currently allocated from the underlying arena (the absolute cursor, not relative to this scope’s mark). Useful in assertions/tests.

pub fn scope(&mut self) -> Scope<'_, B>

Open a nested scratch scope inside this one. The inner scope reclaims only what it allocated when it drops; this outer scope is untouched.

Trait Implementations

impl<'a, B: FixedRange> Drop for Scope<'a, B>

fn drop(&mut self)

Executes the destructor for this type.

fn pin_drop(self: Pin<&mut Self>)

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

Execute the destructor for this type, but different to Drop::drop, it requires self to be pinned.