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-rw-r--r--rust/alloc/vec/spec_extend.rs174
1 files changed, 174 insertions, 0 deletions
diff --git a/rust/alloc/vec/spec_extend.rs b/rust/alloc/vec/spec_extend.rs
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+// SPDX-License-Identifier: Apache-2.0 OR MIT
+
+use crate::alloc::Allocator;
+use crate::collections::{TryReserveError, TryReserveErrorKind};
+use core::iter::TrustedLen;
+use core::ptr::{self};
+use core::slice::{self};
+
+use super::{IntoIter, SetLenOnDrop, Vec};
+
+// Specialization trait used for Vec::extend
+#[cfg(not(no_global_oom_handling))]
+pub(super) trait SpecExtend<T, I> {
+ fn spec_extend(&mut self, iter: I);
+}
+
+// Specialization trait used for Vec::try_extend
+pub(super) trait TrySpecExtend<T, I> {
+ fn try_spec_extend(&mut self, iter: I) -> Result<(), TryReserveError>;
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T, I, A: Allocator> SpecExtend<T, I> for Vec<T, A>
+where
+ I: Iterator<Item = T>,
+{
+ default fn spec_extend(&mut self, iter: I) {
+ self.extend_desugared(iter)
+ }
+}
+
+impl<T, I, A: Allocator> TrySpecExtend<T, I> for Vec<T, A>
+where
+ I: Iterator<Item = T>,
+{
+ default fn try_spec_extend(&mut self, iter: I) -> Result<(), TryReserveError> {
+ self.try_extend_desugared(iter)
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T, I, A: Allocator> SpecExtend<T, I> for Vec<T, A>
+where
+ I: TrustedLen<Item = T>,
+{
+ default fn spec_extend(&mut self, iterator: I) {
+ // This is the case for a TrustedLen iterator.
+ let (low, high) = iterator.size_hint();
+ if let Some(additional) = high {
+ debug_assert_eq!(
+ low,
+ additional,
+ "TrustedLen iterator's size hint is not exact: {:?}",
+ (low, high)
+ );
+ self.reserve(additional);
+ unsafe {
+ let mut ptr = self.as_mut_ptr().add(self.len());
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+ iterator.for_each(move |element| {
+ ptr::write(ptr, element);
+ ptr = ptr.offset(1);
+ // Since the loop executes user code which can panic we have to bump the pointer
+ // after each step.
+ // NB can't overflow since we would have had to alloc the address space
+ local_len.increment_len(1);
+ });
+ }
+ } else {
+ // Per TrustedLen contract a `None` upper bound means that the iterator length
+ // truly exceeds usize::MAX, which would eventually lead to a capacity overflow anyway.
+ // Since the other branch already panics eagerly (via `reserve()`) we do the same here.
+ // This avoids additional codegen for a fallback code path which would eventually
+ // panic anyway.
+ panic!("capacity overflow");
+ }
+ }
+}
+
+impl<T, I, A: Allocator> TrySpecExtend<T, I> for Vec<T, A>
+where
+ I: TrustedLen<Item = T>,
+{
+ default fn try_spec_extend(&mut self, iterator: I) -> Result<(), TryReserveError> {
+ // This is the case for a TrustedLen iterator.
+ let (low, high) = iterator.size_hint();
+ if let Some(additional) = high {
+ debug_assert_eq!(
+ low,
+ additional,
+ "TrustedLen iterator's size hint is not exact: {:?}",
+ (low, high)
+ );
+ self.try_reserve(additional)?;
+ unsafe {
+ let mut ptr = self.as_mut_ptr().add(self.len());
+ let mut local_len = SetLenOnDrop::new(&mut self.len);
+ iterator.for_each(move |element| {
+ ptr::write(ptr, element);
+ ptr = ptr.offset(1);
+ // Since the loop executes user code which can panic we have to bump the pointer
+ // after each step.
+ // NB can't overflow since we would have had to alloc the address space
+ local_len.increment_len(1);
+ });
+ }
+ Ok(())
+ } else {
+ Err(TryReserveErrorKind::CapacityOverflow.into())
+ }
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<T, A: Allocator> SpecExtend<T, IntoIter<T>> for Vec<T, A> {
+ fn spec_extend(&mut self, mut iterator: IntoIter<T>) {
+ unsafe {
+ self.append_elements(iterator.as_slice() as _);
+ }
+ iterator.forget_remaining_elements();
+ }
+}
+
+impl<T, A: Allocator> TrySpecExtend<T, IntoIter<T>> for Vec<T, A> {
+ fn try_spec_extend(&mut self, mut iterator: IntoIter<T>) -> Result<(), TryReserveError> {
+ unsafe {
+ self.try_append_elements(iterator.as_slice() as _)?;
+ }
+ iterator.forget_remaining_elements();
+ Ok(())
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<'a, T: 'a, I, A: Allocator + 'a> SpecExtend<&'a T, I> for Vec<T, A>
+where
+ I: Iterator<Item = &'a T>,
+ T: Clone,
+{
+ default fn spec_extend(&mut self, iterator: I) {
+ self.spec_extend(iterator.cloned())
+ }
+}
+
+impl<'a, T: 'a, I, A: Allocator + 'a> TrySpecExtend<&'a T, I> for Vec<T, A>
+where
+ I: Iterator<Item = &'a T>,
+ T: Clone,
+{
+ default fn try_spec_extend(&mut self, iterator: I) -> Result<(), TryReserveError> {
+ self.try_spec_extend(iterator.cloned())
+ }
+}
+
+#[cfg(not(no_global_oom_handling))]
+impl<'a, T: 'a, A: Allocator + 'a> SpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
+where
+ T: Copy,
+{
+ fn spec_extend(&mut self, iterator: slice::Iter<'a, T>) {
+ let slice = iterator.as_slice();
+ unsafe { self.append_elements(slice) };
+ }
+}
+
+impl<'a, T: 'a, A: Allocator + 'a> TrySpecExtend<&'a T, slice::Iter<'a, T>> for Vec<T, A>
+where
+ T: Copy,
+{
+ fn try_spec_extend(&mut self, iterator: slice::Iter<'a, T>) -> Result<(), TryReserveError> {
+ let slice = iterator.as_slice();
+ unsafe { self.try_append_elements(slice) }
+ }
+}