Expand description
Where the pieces of a container sit, worked out in one place so that the builder and the reader cannot drift apart.
+--------+--------------+---------------+------------+--------------+
| header | key entries | value entries | key region | value region |
| 4 | objects only | 8 per element | | |
+--------+--------------+---------------+------------+--------------+A key entry is four bytes, an offset into the container, and a key’s length is the difference between its offset and the next one. An interned object’s key entries are two byte ids instead, padded up so that the value entries stay on a four byte stride.
A value entry is eight bytes: a copy of the element’s own header, so that a scan over the entries never touches the value region, and the offset the element starts at. Offsets are relative to the container’s header, so a container can be copied anywhere without rewriting it.
Values are stored in entry order and tile the value region, which is what makes the last entry enough to work out the whole container’s length.