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-// SPDX-License-Identifier: Apache-2.0 OR MIT
-
-#![unstable(feature = "raw_vec_internals", reason = "unstable const warnings", issue = "none")]
-
-use core::alloc::LayoutError;
-use core::cmp;
-use core::intrinsics;
-use core::mem::{self, ManuallyDrop, MaybeUninit, SizedTypeProperties};
-use core::ptr::{self, NonNull, Unique};
-use core::slice;
-
-#[cfg(not(no_global_oom_handling))]
-use crate::alloc::handle_alloc_error;
-use crate::alloc::{Allocator, Global, Layout};
-use crate::boxed::Box;
-use crate::collections::TryReserveError;
-use crate::collections::TryReserveErrorKind::*;
-
-#[cfg(test)]
-mod tests;
-
-enum AllocInit {
- /// The contents of the new memory are uninitialized.
- Uninitialized,
- /// The new memory is guaranteed to be zeroed.
- #[allow(dead_code)]
- Zeroed,
-}
-
-#[repr(transparent)]
-#[cfg_attr(target_pointer_width = "16", rustc_layout_scalar_valid_range_end(0x7fff))]
-#[cfg_attr(target_pointer_width = "32", rustc_layout_scalar_valid_range_end(0x7fff_ffff))]
-#[cfg_attr(target_pointer_width = "64", rustc_layout_scalar_valid_range_end(0x7fff_ffff_ffff_ffff))]
-struct Cap(usize);
-
-impl Cap {
- const ZERO: Cap = unsafe { Cap(0) };
-}
-
-/// A low-level utility for more ergonomically allocating, reallocating, and deallocating
-/// a buffer of memory on the heap without having to worry about all the corner cases
-/// involved. This type is excellent for building your own data structures like Vec and VecDeque.
-/// In particular:
-///
-/// * Produces `Unique::dangling()` on zero-sized types.
-/// * Produces `Unique::dangling()` on zero-length allocations.
-/// * Avoids freeing `Unique::dangling()`.
-/// * Catches all overflows in capacity computations (promotes them to "capacity overflow" panics).
-/// * Guards against 32-bit systems allocating more than isize::MAX bytes.
-/// * Guards against overflowing your length.
-/// * Calls `handle_alloc_error` for fallible allocations.
-/// * Contains a `ptr::Unique` and thus endows the user with all related benefits.
-/// * Uses the excess returned from the allocator to use the largest available capacity.
-///
-/// This type does not in anyway inspect the memory that it manages. When dropped it *will*
-/// free its memory, but it *won't* try to drop its contents. It is up to the user of `RawVec`
-/// to handle the actual things *stored* inside of a `RawVec`.
-///
-/// Note that the excess of a zero-sized types is always infinite, so `capacity()` always returns
-/// `usize::MAX`. This means that you need to be careful when round-tripping this type with a
-/// `Box<[T]>`, since `capacity()` won't yield the length.
-#[allow(missing_debug_implementations)]
-pub(crate) struct RawVec<T, A: Allocator = Global> {
- ptr: Unique<T>,
- /// Never used for ZSTs; it's `capacity()`'s responsibility to return usize::MAX in that case.
- ///
- /// # Safety
- ///
- /// `cap` must be in the `0..=isize::MAX` range.
- cap: Cap,
- alloc: A,
-}
-
-impl<T> RawVec<T, Global> {
- /// HACK(Centril): This exists because stable `const fn` can only call stable `const fn`, so
- /// they cannot call `Self::new()`.
- ///
- /// If you change `RawVec<T>::new` or dependencies, please take care to not introduce anything
- /// that would truly const-call something unstable.
- pub const NEW: Self = Self::new();
-
- /// Creates the biggest possible `RawVec` (on the system heap)
- /// without allocating. If `T` has positive size, then this makes a
- /// `RawVec` with capacity `0`. If `T` is zero-sized, then it makes a
- /// `RawVec` with capacity `usize::MAX`. Useful for implementing
- /// delayed allocation.
- #[must_use]
- pub const fn new() -> Self {
- Self::new_in(Global)
- }
-
- /// Creates a `RawVec` (on the system heap) with exactly the
- /// capacity and alignment requirements for a `[T; capacity]`. This is
- /// equivalent to calling `RawVec::new` when `capacity` is `0` or `T` is
- /// zero-sized. Note that if `T` is zero-sized this means you will
- /// *not* get a `RawVec` with the requested capacity.
- ///
- /// # Panics
- ///
- /// Panics if the requested capacity exceeds `isize::MAX` bytes.
- ///
- /// # Aborts
- ///
- /// Aborts on OOM.
- #[cfg(not(any(no_global_oom_handling, test)))]
- #[must_use]
- #[inline]
- pub fn with_capacity(capacity: usize) -> Self {
- Self::with_capacity_in(capacity, Global)
- }
-
- /// Like `with_capacity`, but guarantees the buffer is zeroed.
- #[cfg(not(any(no_global_oom_handling, test)))]
- #[must_use]
- #[inline]
- pub fn with_capacity_zeroed(capacity: usize) -> Self {
- Self::with_capacity_zeroed_in(capacity, Global)
- }
-}
-
-impl<T, A: Allocator> RawVec<T, A> {
- // Tiny Vecs are dumb. Skip to:
- // - 8 if the element size is 1, because any heap allocators is likely
- // to round up a request of less than 8 bytes to at least 8 bytes.
- // - 4 if elements are moderate-sized (<= 1 KiB).
- // - 1 otherwise, to avoid wasting too much space for very short Vecs.
- pub(crate) const MIN_NON_ZERO_CAP: usize = if mem::size_of::<T>() == 1 {
- 8
- } else if mem::size_of::<T>() <= 1024 {
- 4
- } else {
- 1
- };
-
- /// Like `new`, but parameterized over the choice of allocator for
- /// the returned `RawVec`.
- pub const fn new_in(alloc: A) -> Self {
- // `cap: 0` means "unallocated". zero-sized types are ignored.
- Self { ptr: Unique::dangling(), cap: Cap::ZERO, alloc }
- }
-
- /// Like `with_capacity`, but parameterized over the choice of
- /// allocator for the returned `RawVec`.
- #[cfg(not(no_global_oom_handling))]
- #[inline]
- pub fn with_capacity_in(capacity: usize, alloc: A) -> Self {
- Self::allocate_in(capacity, AllocInit::Uninitialized, alloc)
- }
-
- /// Like `try_with_capacity`, but parameterized over the choice of
- /// allocator for the returned `RawVec`.
- #[inline]
- pub fn try_with_capacity_in(capacity: usize, alloc: A) -> Result<Self, TryReserveError> {
- Self::try_allocate_in(capacity, AllocInit::Uninitialized, alloc)
- }
-
- /// Like `with_capacity_zeroed`, but parameterized over the choice
- /// of allocator for the returned `RawVec`.
- #[cfg(not(no_global_oom_handling))]
- #[inline]
- pub fn with_capacity_zeroed_in(capacity: usize, alloc: A) -> Self {
- Self::allocate_in(capacity, AllocInit::Zeroed, alloc)
- }
-
- /// Converts the entire buffer into `Box<[MaybeUninit<T>]>` with the specified `len`.
- ///
- /// Note that this will correctly reconstitute any `cap` changes
- /// that may have been performed. (See description of type for details.)
- ///
- /// # Safety
- ///
- /// * `len` must be greater than or equal to the most recently requested capacity, and
- /// * `len` must be less than or equal to `self.capacity()`.
- ///
- /// Note, that the requested capacity and `self.capacity()` could differ, as
- /// an allocator could overallocate and return a greater memory block than requested.
- pub unsafe fn into_box(self, len: usize) -> Box<[MaybeUninit<T>], A> {
- // Sanity-check one half of the safety requirement (we cannot check the other half).
- debug_assert!(
- len <= self.capacity(),
- "`len` must be smaller than or equal to `self.capacity()`"
- );
-
- let me = ManuallyDrop::new(self);
- unsafe {
- let slice = slice::from_raw_parts_mut(me.ptr() as *mut MaybeUninit<T>, len);
- Box::from_raw_in(slice, ptr::read(&me.alloc))
- }
- }
-
- #[cfg(not(no_global_oom_handling))]
- fn allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Self {
- // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
- if T::IS_ZST || capacity == 0 {
- Self::new_in(alloc)
- } else {
- // We avoid `unwrap_or_else` here because it bloats the amount of
- // LLVM IR generated.
- let layout = match Layout::array::<T>(capacity) {
- Ok(layout) => layout,
- Err(_) => capacity_overflow(),
- };
- match alloc_guard(layout.size()) {
- Ok(_) => {}
- Err(_) => capacity_overflow(),
- }
- let result = match init {
- AllocInit::Uninitialized => alloc.allocate(layout),
- AllocInit::Zeroed => alloc.allocate_zeroed(layout),
- };
- let ptr = match result {
- Ok(ptr) => ptr,
- Err(_) => handle_alloc_error(layout),
- };
-
- // Allocators currently return a `NonNull<[u8]>` whose length
- // matches the size requested. If that ever changes, the capacity
- // here should change to `ptr.len() / mem::size_of::<T>()`.
- Self {
- ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
- cap: unsafe { Cap(capacity) },
- alloc,
- }
- }
- }
-
- fn try_allocate_in(capacity: usize, init: AllocInit, alloc: A) -> Result<Self, TryReserveError> {
- // Don't allocate here because `Drop` will not deallocate when `capacity` is 0.
- if T::IS_ZST || capacity == 0 {
- return Ok(Self::new_in(alloc));
- }
-
- let layout = Layout::array::<T>(capacity).map_err(|_| CapacityOverflow)?;
- alloc_guard(layout.size())?;
- let result = match init {
- AllocInit::Uninitialized => alloc.allocate(layout),
- AllocInit::Zeroed => alloc.allocate_zeroed(layout),
- };
- let ptr = result.map_err(|_| AllocError { layout, non_exhaustive: () })?;
-
- // Allocators currently return a `NonNull<[u8]>` whose length
- // matches the size requested. If that ever changes, the capacity
- // here should change to `ptr.len() / mem::size_of::<T>()`.
- Ok(Self {
- ptr: unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) },
- cap: unsafe { Cap(capacity) },
- alloc,
- })
- }
-
- /// Reconstitutes a `RawVec` from a pointer, capacity, and allocator.
- ///
- /// # Safety
- ///
- /// The `ptr` must be allocated (via the given allocator `alloc`), and with the given
- /// `capacity`.
- /// The `capacity` cannot exceed `isize::MAX` for sized types. (only a concern on 32-bit
- /// systems). For ZSTs capacity is ignored.
- /// If the `ptr` and `capacity` come from a `RawVec` created via `alloc`, then this is
- /// guaranteed.
- #[inline]
- pub unsafe fn from_raw_parts_in(ptr: *mut T, capacity: usize, alloc: A) -> Self {
- let cap = if T::IS_ZST { Cap::ZERO } else { unsafe { Cap(capacity) } };
- Self { ptr: unsafe { Unique::new_unchecked(ptr) }, cap, alloc }
- }
-
- /// Gets a raw pointer to the start of the allocation. Note that this is
- /// `Unique::dangling()` if `capacity == 0` or `T` is zero-sized. In the former case, you must
- /// be careful.
- #[inline]
- pub fn ptr(&self) -> *mut T {
- self.ptr.as_ptr()
- }
-
- /// Gets the capacity of the allocation.
- ///
- /// This will always be `usize::MAX` if `T` is zero-sized.
- #[inline(always)]
- pub fn capacity(&self) -> usize {
- if T::IS_ZST { usize::MAX } else { self.cap.0 }
- }
-
- /// Returns a shared reference to the allocator backing this `RawVec`.
- pub fn allocator(&self) -> &A {
- &self.alloc
- }
-
- fn current_memory(&self) -> Option<(NonNull<u8>, Layout)> {
- if T::IS_ZST || self.cap.0 == 0 {
- None
- } else {
- // We could use Layout::array here which ensures the absence of isize and usize overflows
- // and could hypothetically handle differences between stride and size, but this memory
- // has already been allocated so we know it can't overflow and currently rust does not
- // support such types. So we can do better by skipping some checks and avoid an unwrap.
- let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) };
- unsafe {
- let align = mem::align_of::<T>();
- let size = mem::size_of::<T>().unchecked_mul(self.cap.0);
- let layout = Layout::from_size_align_unchecked(size, align);
- Some((self.ptr.cast().into(), layout))
- }
- }
- }
-
- /// Ensures that the buffer contains at least enough space to hold `len +
- /// additional` elements. If it doesn't already have enough capacity, will
- /// reallocate enough space plus comfortable slack space to get amortized
- /// *O*(1) behavior. Will limit this behavior if it would needlessly cause
- /// itself to panic.
- ///
- /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
- /// the requested space. This is not really unsafe, but the unsafe
- /// code *you* write that relies on the behavior of this function may break.
- ///
- /// This is ideal for implementing a bulk-push operation like `extend`.
- ///
- /// # Panics
- ///
- /// Panics if the new capacity exceeds `isize::MAX` bytes.
- ///
- /// # Aborts
- ///
- /// Aborts on OOM.
- #[cfg(not(no_global_oom_handling))]
- #[inline]
- pub fn reserve(&mut self, len: usize, additional: usize) {
- // Callers expect this function to be very cheap when there is already sufficient capacity.
- // Therefore, we move all the resizing and error-handling logic from grow_amortized and
- // handle_reserve behind a call, while making sure that this function is likely to be
- // inlined as just a comparison and a call if the comparison fails.
- #[cold]
- fn do_reserve_and_handle<T, A: Allocator>(
- slf: &mut RawVec<T, A>,
- len: usize,
- additional: usize,
- ) {
- handle_reserve(slf.grow_amortized(len, additional));
- }
-
- if self.needs_to_grow(len, additional) {
- do_reserve_and_handle(self, len, additional);
- }
- }
-
- /// A specialized version of `reserve()` used only by the hot and
- /// oft-instantiated `Vec::push()`, which does its own capacity check.
- #[cfg(not(no_global_oom_handling))]
- #[inline(never)]
- pub fn reserve_for_push(&mut self, len: usize) {
- handle_reserve(self.grow_amortized(len, 1));
- }
-
- /// The same as `reserve`, but returns on errors instead of panicking or aborting.
- pub fn try_reserve(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
- if self.needs_to_grow(len, additional) {
- self.grow_amortized(len, additional)?;
- }
- unsafe {
- // Inform the optimizer that the reservation has succeeded or wasn't needed
- core::intrinsics::assume(!self.needs_to_grow(len, additional));
- }
- Ok(())
- }
-
- /// The same as `reserve_for_push`, but returns on errors instead of panicking or aborting.
- #[inline(never)]
- pub fn try_reserve_for_push(&mut self, len: usize) -> Result<(), TryReserveError> {
- self.grow_amortized(len, 1)
- }
-
- /// Ensures that the buffer contains at least enough space to hold `len +
- /// additional` elements. If it doesn't already, will reallocate the
- /// minimum possible amount of memory necessary. Generally this will be
- /// exactly the amount of memory necessary, but in principle the allocator
- /// is free to give back more than we asked for.
- ///
- /// If `len` exceeds `self.capacity()`, this may fail to actually allocate
- /// the requested space. This is not really unsafe, but the unsafe code
- /// *you* write that relies on the behavior of this function may break.
- ///
- /// # Panics
- ///
- /// Panics if the new capacity exceeds `isize::MAX` bytes.
- ///
- /// # Aborts
- ///
- /// Aborts on OOM.
- #[cfg(not(no_global_oom_handling))]
- pub fn reserve_exact(&mut self, len: usize, additional: usize) {
- handle_reserve(self.try_reserve_exact(len, additional));
- }
-
- /// The same as `reserve_exact`, but returns on errors instead of panicking or aborting.
- pub fn try_reserve_exact(
- &mut self,
- len: usize,
- additional: usize,
- ) -> Result<(), TryReserveError> {
- if self.needs_to_grow(len, additional) {
- self.grow_exact(len, additional)?;
- }
- unsafe {
- // Inform the optimizer that the reservation has succeeded or wasn't needed
- core::intrinsics::assume(!self.needs_to_grow(len, additional));
- }
- Ok(())
- }
-
- /// Shrinks the buffer down to the specified capacity. If the given amount
- /// is 0, actually completely deallocates.
- ///
- /// # Panics
- ///
- /// Panics if the given amount is *larger* than the current capacity.
- ///
- /// # Aborts
- ///
- /// Aborts on OOM.
- #[cfg(not(no_global_oom_handling))]
- pub fn shrink_to_fit(&mut self, cap: usize) {
- handle_reserve(self.shrink(cap));
- }
-}
-
-impl<T, A: Allocator> RawVec<T, A> {
- /// Returns if the buffer needs to grow to fulfill the needed extra capacity.
- /// Mainly used to make inlining reserve-calls possible without inlining `grow`.
- fn needs_to_grow(&self, len: usize, additional: usize) -> bool {
- additional > self.capacity().wrapping_sub(len)
- }
-
- /// # Safety:
- ///
- /// `cap` must not exceed `isize::MAX`.
- unsafe fn set_ptr_and_cap(&mut self, ptr: NonNull<[u8]>, cap: usize) {
- // Allocators currently return a `NonNull<[u8]>` whose length matches
- // the size requested. If that ever changes, the capacity here should
- // change to `ptr.len() / mem::size_of::<T>()`.
- self.ptr = unsafe { Unique::new_unchecked(ptr.cast().as_ptr()) };
- self.cap = unsafe { Cap(cap) };
- }
-
- // This method is usually instantiated many times. So we want it to be as
- // small as possible, to improve compile times. But we also want as much of
- // its contents to be statically computable as possible, to make the
- // generated code run faster. Therefore, this method is carefully written
- // so that all of the code that depends on `T` is within it, while as much
- // of the code that doesn't depend on `T` as possible is in functions that
- // are non-generic over `T`.
- fn grow_amortized(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
- // This is ensured by the calling contexts.
- debug_assert!(additional > 0);
-
- if T::IS_ZST {
- // Since we return a capacity of `usize::MAX` when `elem_size` is
- // 0, getting to here necessarily means the `RawVec` is overfull.
- return Err(CapacityOverflow.into());
- }
-
- // Nothing we can really do about these checks, sadly.
- let required_cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
-
- // This guarantees exponential growth. The doubling cannot overflow
- // because `cap <= isize::MAX` and the type of `cap` is `usize`.
- let cap = cmp::max(self.cap.0 * 2, required_cap);
- let cap = cmp::max(Self::MIN_NON_ZERO_CAP, cap);
-
- let new_layout = Layout::array::<T>(cap);
-
- // `finish_grow` is non-generic over `T`.
- let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
- // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than isize::MAX items
- unsafe { self.set_ptr_and_cap(ptr, cap) };
- Ok(())
- }
-
- // The constraints on this method are much the same as those on
- // `grow_amortized`, but this method is usually instantiated less often so
- // it's less critical.
- fn grow_exact(&mut self, len: usize, additional: usize) -> Result<(), TryReserveError> {
- if T::IS_ZST {
- // Since we return a capacity of `usize::MAX` when the type size is
- // 0, getting to here necessarily means the `RawVec` is overfull.
- return Err(CapacityOverflow.into());
- }
-
- let cap = len.checked_add(additional).ok_or(CapacityOverflow)?;
- let new_layout = Layout::array::<T>(cap);
-
- // `finish_grow` is non-generic over `T`.
- let ptr = finish_grow(new_layout, self.current_memory(), &mut self.alloc)?;
- // SAFETY: finish_grow would have resulted in a capacity overflow if we tried to allocate more than isize::MAX items
- unsafe {
- self.set_ptr_and_cap(ptr, cap);
- }
- Ok(())
- }
-
- #[cfg(not(no_global_oom_handling))]
- fn shrink(&mut self, cap: usize) -> Result<(), TryReserveError> {
- assert!(cap <= self.capacity(), "Tried to shrink to a larger capacity");
-
- let (ptr, layout) = if let Some(mem) = self.current_memory() { mem } else { return Ok(()) };
- // See current_memory() why this assert is here
- let _: () = const { assert!(mem::size_of::<T>() % mem::align_of::<T>() == 0) };
-
- // If shrinking to 0, deallocate the buffer. We don't reach this point
- // for the T::IS_ZST case since current_memory() will have returned
- // None.
- if cap == 0 {
- unsafe { self.alloc.deallocate(ptr, layout) };
- self.ptr = Unique::dangling();
- self.cap = Cap::ZERO;
- } else {
- let ptr = unsafe {
- // `Layout::array` cannot overflow here because it would have
- // overflowed earlier when capacity was larger.
- let new_size = mem::size_of::<T>().unchecked_mul(cap);
- let new_layout = Layout::from_size_align_unchecked(new_size, layout.align());
- self.alloc
- .shrink(ptr, layout, new_layout)
- .map_err(|_| AllocError { layout: new_layout, non_exhaustive: () })?
- };
- // SAFETY: if the allocation is valid, then the capacity is too
- unsafe {
- self.set_ptr_and_cap(ptr, cap);
- }
- }
- Ok(())
- }
-}
-
-// This function is outside `RawVec` to minimize compile times. See the comment
-// above `RawVec::grow_amortized` for details. (The `A` parameter isn't
-// significant, because the number of different `A` types seen in practice is
-// much smaller than the number of `T` types.)
-#[inline(never)]
-fn finish_grow<A>(
- new_layout: Result<Layout, LayoutError>,
- current_memory: Option<(NonNull<u8>, Layout)>,
- alloc: &mut A,
-) -> Result<NonNull<[u8]>, TryReserveError>
-where
- A: Allocator,
-{
- // Check for the error here to minimize the size of `RawVec::grow_*`.
- let new_layout = new_layout.map_err(|_| CapacityOverflow)?;
-
- alloc_guard(new_layout.size())?;
-
- let memory = if let Some((ptr, old_layout)) = current_memory {
- debug_assert_eq!(old_layout.align(), new_layout.align());
- unsafe {
- // The allocator checks for alignment equality
- intrinsics::assume(old_layout.align() == new_layout.align());
- alloc.grow(ptr, old_layout, new_layout)
- }
- } else {
- alloc.allocate(new_layout)
- };
-
- memory.map_err(|_| AllocError { layout: new_layout, non_exhaustive: () }.into())
-}
-
-unsafe impl<#[may_dangle] T, A: Allocator> Drop for RawVec<T, A> {
- /// Frees the memory owned by the `RawVec` *without* trying to drop its contents.
- fn drop(&mut self) {
- if let Some((ptr, layout)) = self.current_memory() {
- unsafe { self.alloc.deallocate(ptr, layout) }
- }
- }
-}
-
-// Central function for reserve error handling.
-#[cfg(not(no_global_oom_handling))]
-#[inline]
-fn handle_reserve(result: Result<(), TryReserveError>) {
- match result.map_err(|e| e.kind()) {
- Err(CapacityOverflow) => capacity_overflow(),
- Err(AllocError { layout, .. }) => handle_alloc_error(layout),
- Ok(()) => { /* yay */ }
- }
-}
-
-// We need to guarantee the following:
-// * We don't ever allocate `> isize::MAX` byte-size objects.
-// * We don't overflow `usize::MAX` and actually allocate too little.
-//
-// On 64-bit we just need to check for overflow since trying to allocate
-// `> isize::MAX` bytes will surely fail. On 32-bit and 16-bit we need to add
-// an extra guard for this in case we're running on a platform which can use
-// all 4GB in user-space, e.g., PAE or x32.
-
-#[inline]
-fn alloc_guard(alloc_size: usize) -> Result<(), TryReserveError> {
- if usize::BITS < 64 && alloc_size > isize::MAX as usize {
- Err(CapacityOverflow.into())
- } else {
- Ok(())
- }
-}
-
-// One central function responsible for reporting capacity overflows. This'll
-// ensure that the code generation related to these panics is minimal as there's
-// only one location which panics rather than a bunch throughout the module.
-#[cfg(not(no_global_oom_handling))]
-#[cfg_attr(not(feature = "panic_immediate_abort"), inline(never))]
-fn capacity_overflow() -> ! {
- panic!("capacity overflow");
-}