If you are reading 1000 lines from stdin at once to separate Strings, you are already going to be accessing memory in 1000 places at the same time, and making it 1001 isn't meaningfully worse for your cache. (Implementation would be Vec<String>, which would lay out the 1000 headers contiguously.)

But I genuinely have a hard time understanding for what kind of workload I would ever do that. If you want to read a 1000 lines of stdin, and cannot use an iterator and must work on them at the same time, I would likely much rather read them into a single string and then split that into a 1000 &str using the .lines() iterator.

I was miffed at: 1000 lines from stdin. It’s the same problem 1000 times, not 1000 problems at once.

Presumably the idea is, for example, sorting? In which case you do have to read the entire input before you can do anything. But the way I'd do that is to read the entire stdin to a single String, then work with &str pointers to it.