Worth noting that the metadata structure can be done more efficiently with a flexible array member, but it requires alignment to alignof(max_align_t) to obey th

Worth noting that the metadata structure can be done more efficiently with a flexible array member, but it requires alignment to alignof(max_align_t) to obey the ABI. The structure will consume the same amount of memory (16 bytes on x86-64) but you avoid a dereference and you have an extra pointer worth of space to use for whatever.