> They're not a runtime construct, they have zero influence over what code does at run time (e.g. mrustc compiler doesn't implement lifetimes, but bootstraps the whole Rust compiler just fine).
This kind of reasoning seems like it makes sense, but actually it is false. ("Modern C++" people make the same arguments when arguing that you should use "zero-cost abstractions" all over the place). Abstractions determine how people write code, and the way they write the code determines the performance of the code.
When you conceptualize a bunch of stuff as different objects with different lifetimes, you are going to write code treating stuff as different objects with different lifetimes. That is slow.
> If you create `Vec<Object>` in Rust, then all objects will be allocated and laid out together as one contiguous chunk of memory
Sure, and that covers a small percentage of the use cases I am talking about, but not most of them.
This kind of reasoning seems like it makes sense, but actually it is false. ("Modern C++" people make the same arguments when arguing that you should use "zero-cost abstractions" all over the place). Abstractions determine how people write code, and the way they write the code determines the performance of the code.
When you conceptualize a bunch of stuff as different objects with different lifetimes, you are going to write code treating stuff as different objects with different lifetimes. That is slow.
> If you create `Vec<Object>` in Rust, then all objects will be allocated and laid out together as one contiguous chunk of memory
Sure, and that covers a small percentage of the use cases I am talking about, but not most of them.