> You do need efficient data structures, which often implies developing custom ones for specific use cases.
You are assuming you can't do this with those vecs/maps. But you can! That's what the "additional semantics" are.
They will be slightly slower due to often using indexes instead of raw pointer, which requires a bound check and an addition to get the pointer, and sometimes a reallocation, but they won't be that slow. Surely they will be faster than C#, which you claim can implement those same data structures efficiently. You also often get the benefit of better cache locality due to packing everything together, meaning it could even be faster.
> They will be slightly slower due to often using indexes instead of raw pointer, which requires a bound check and an addition to get the pointer, and sometimes a reallocation, but they won't be that slow.
This is not a fundamental requirement, though. Assuming arena-like behavior, the index will be constructed/provided by the arena itself, so the bounds check can be safely ellided by-construction. Reallocation cost of the entire arena could be expensive, but if that is a cost you'd want to ammortize down to a new allocation, the arena could be implemented as an extensible list of non-growable arenas: every time an arena is full, you append another. This can be an issue if you don't keep track of deletions/tombstones or can't afford a compaction step to keep memory usage down, but in practice having all of these requirements at once is not as common.
You are assuming you can't do this with those vecs/maps. But you can! That's what the "additional semantics" are.
They will be slightly slower due to often using indexes instead of raw pointer, which requires a bound check and an addition to get the pointer, and sometimes a reallocation, but they won't be that slow. Surely they will be faster than C#, which you claim can implement those same data structures efficiently. You also often get the benefit of better cache locality due to packing everything together, meaning it could even be faster.