CxxVector: implement reserve() and capacity() #1300
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dtolnay
reviewed
Aug 10, 2025
| begin_function_definition(out); | ||
| writeln!( | ||
| out, | ||
| "void cxxbridge1$std$vector${}$reserve(::std::vector<{}> *s, ::std::size_t new_cap) {{", |
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Whether or not the underlying C++ API can throw an exception, this needs a noexcept to block a C++ exception from unwinding across an FFI boundary which is UB.
Suggested change
| "void cxxbridge1$std$vector${}$reserve(::std::vector<{}> *s, ::std::size_t new_cap) {{", | |
| "void cxxbridge1$std$vector${}$reserve(::std::vector<{}> *s, ::std::size_t new_cap) noexcept {{", |
| } | ||
| } | ||
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|
||
| impl<A> Extend<A> for Pin<&mut CxxVector<A>> |
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It is almost always more appropriate to match the type definition's generic parameter names than the trait definition's.
Suggested change
| impl<A> Extend<A> for Pin<&mut CxxVector<A>> | |
| impl<T> Extend<T> for Pin<&mut CxxVector<T>> |
| unsafe fn __get_unchecked(v: *mut CxxVector<$ty>, pos: usize) -> *mut $ty { | ||
| extern "C" { | ||
| #[link_name = concat!("cxxbridge1$std$vector$", $segment, "$get_unchecked")] | ||
| fn __get_unchecked(_: *mut CxxVector<$ty>, _: usize) -> *mut $ty; | ||
| } | ||
| unsafe { __get_unchecked(v, pos) } | ||
| } | ||
| unsafe fn __reserve(v: Pin<&mut CxxVector<$ty>>, pos: usize) { |
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Suggested change
| unsafe fn __reserve(v: Pin<&mut CxxVector<$ty>>, pos: usize) { | |
| unsafe fn __reserve(v: Pin<&mut CxxVector<$ty>>, new_cap: usize) { |
| unsafe fn __get_unchecked(v: *mut CxxVector<Self>, pos: usize) -> *mut Self; | ||
| #[doc(hidden)] | ||
| unsafe fn __reserve(v: Pin<&mut CxxVector<Self>>, new_capacity: usize); |
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This is called new_cap everywhere else.
Suggested change
| unsafe fn __reserve(v: Pin<&mut CxxVector<Self>>, new_capacity: usize); | |
| unsafe fn __reserve(v: Pin<&mut CxxVector<Self>>, new_cap: usize); |
| pub fn reserve(self: Pin<&mut Self>, additional: usize) { | ||
| unsafe { | ||
| let len = self.as_ref().len(); | ||
| T::__reserve(self, len + additional); |
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This is unsound without checked addition. As written, something like vector.reserve(usize::MAX) will silently do nothing in release mode where arithmetic overflow checks are off and the addition wraps.
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Efficient insertions into CxxVector requires reserving additional capacity. This also adds a way to query current capacity.
Also implement
extend, which can use the size hint