orx-pinned-vec

PinnedVec trait serves as the marker with common vector functionalities for vector implementations which

• preserves the memory locations of their elements; i.e., keeps them pinned.

This feature eliminates a specific set of errors leading to undefined behavior (UB), and hence, allows to work with a more flexible borrow checker. Consider for instance the following code block which does not compile.

let mut vec = Vec::with_capacity(2);
vec.extend_from_slice(&[0, 1]);
let ref0 = &vec[0];
vec.push(2);
// let value0 = *ref0; // does not compile!

Note that we have not removed any elements form the vector. The reason why dereferencing ref0 causes UB is:

• the call to push element 2 to the vector requires the vector to grow,
• the standard vector might (or might not) carry the data to another memory location,
• in that case, ref0 is invalid which causes the UB.

PinnedVec implementations, on the other hand, guarantee that such moves in memory locations do not happen; and hence, eliminating the cause of the UB observed here.

See, FixedVec and SplitVec for two basic pinned-vector implementations.

Further, see ImpVec crate which allows converting any PinnedVec implementation into an imp-vec. An imp-vec stands for immutable-push-vector, literally allowing to push to the vector with an immutable reference. This turns out to be a very useful opeartion, allowing to conveniently implement tricky data structures.