Small Vector Optimization embeds a static array directly inside the vector struct (e.g. 16 or 32 bytes). For small element counts, zero heap allocations occur. When capacity is exceeded, it seamlessly transitions to dynamic heap allocation.

SVO vectors are massive performance wins for short-lived collections like function arguments, AST children nodes, and query result lists. It keeps the data in the CPU L1 cache.

Make sure your union properly handles object lifetime construction via placement new and explicit destructor calls when transitioning between the inline buffer and heap pointer!