A bump allocator cannot free one allocation, but it can free them all at once by rewinding the cursor. Today you add Reset, closing out the bump allocator with the one kind of freeing it supports.
Rewind the cursor to zero so the whole arena is reusable, and confirm the next allocation starts over.
The bump allocator’s great weakness is also its charm: it cannot free a single allocation, because there is no record of where one ended and the next began - just the one cursor. What it can do is free everything at once, by moving the cursor back to 0. After that the whole arena is available again and the next allocation restarts from offset 0.
This “free all or nothing” model is exactly why real programs need more: you want to release one object while keeping its neighbours. Reclaiming individual allocations is impossible without per-block bookkeeping, and building that bookkeeping - a header on every block that records its size and whether it is in use - is the entire next chapter. The bump allocator stays as the honest warm-up: tiny, fast, and useful whenever you truly can throw everything away together.
// the only "free" a bump allocator offers: rewind everythingfunc (a *Arena) Reset() { a.cursor = 0 }// note: Reset does not need to erase the bytes; the next// allocation simply overwrites them