closed_hashing

      +----------------+
      |"(keyi, valuei)"|      "(key, value) pairs are stored directly"
      +----+-----------+      "into the array (no pointers)"
           |                 +--------+---------------------+
           |                 |        |                     |
           |                 |        |                     |
           |                 |        |                     |
           |                 |        |                     |
           |                 |        |                     |
           |                 +--------+---------------------+
           +---------------> | keyi   | valuei              |
            hasher(keyi)     +--------+---------------------+
                             |        |                     |
                             |        |                     |
                             |        |                     |
                             +--------+---------------------+
                             |        |                     |
                             +--------+---------------------+
                             |        |                     |
                             |        |                     |
                             |        |                     |
                             +--------+---------------------+
      
                        absl::flat_hash_map