I think when he said "just do an array of flat records" he meant as opposed to record of arrays (i.e. row oriented vs column oriented), as opposed to fancy data structures which I think you're assuming he was implying. Separate arrays for each data member are common in game engines exactly because they're good for iterating over, which as you said is common.
replyThat's also great for letting the compiler unlock auto-vectorization opportunities without delving into the world of manual SIMD.
replyEven storing something simple such as an array of complex numbers as a structure of arrays (SoA) rather than an array of structures (AoS) can unlock a lot of optimizations. For example, less permutes/shuffles and more arithmetic instructions.
Depending on how many fields you actually need when you iterate over the data, you prevent cache pollution as well.
Jonathan Blow's own unreleased Jai programming language has a feature to make it trivial to switch between array-of-structs and struct-of-arrays.
replyFrom a quick search, it seems HackerNews's own jcelerier has put together a C++ library for doing this. https://github.com/celtera/ahsohtoa
I haven't watched his videos on his language for ages, but this was a big thing he wanted in his language: being able to swap between array-of-structs and struct-of-array quickly and easily.
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