> To explain what I think this comment means. When working on embedded systems, you can interact with hardware devices by writing directly to specially mapped memory areas.

And why can't you do this in rust?

You can. Rust allows full memory addressing.

There's nothing to prevent you from doing this, although you may have to wrap it in an unsafe block.

They're saying more that intrusive data structures are really nice in situations that restrict heap allocation. The memory overhead outside of the structures linked together is O(1), because all of the per object metadata is stored in the objects themselves. That means consumers generally don't have to be hardcoded for certain number of objects like you would for an array/vector that doesn't have access to a heap.