[Someone]

> product types have to be heap-allocated

Conceptually, that’s true, but a compiler is free to do things differently. For example, if escape analysis shows that an object allocated in a block never escapes the block, the optimizer can replace the object by local variables, one for each field in the object.

And that’s not theoretical. https://www.bettercodebytes.com/allocation-elimination-when-..., https://medium.com/@souvanik.saha/are-java-objects-always-cr... show that it (sometimes) does.