...you were asking what's so "exotic" about compact dynamic arrays if they're just deques? I'm telling you they're not deques, because they have additional cons

...you were asking what's so "exotic" about compact dynamic arrays if they're just deques? I'm telling you they're not deques, because they have additional constraints that deques don't have. Are you intentionally twisting this backwards or something? You're basically turning the conversation into something like this: You: "Penguins are birds, right? What's so exotic about penguins when I see all these birds flying around me?" Me: "Penguins live in Antarctica... and don't fly... (hence why people find them exotic...)" You: "But who says birds can't live in Antarctica?? And chickens can't fly either. And penguins are birds. So what's so exotic about penguins?" Me: {what sane response can I even give you here?!} ________________________________________ But anyway... > implies that compact dynamic array can't be used for std::deque, when it is used as such To entertain your new argument here: Deque requires references to existing elements not to be invalidated when new elements are appended. I don't know how compact dynamic arrays work, but dynamic arrays generally move elements around in memory while maintaining guaranteed worst-case O(1)-time access to them, so it seems kind of impossible for them to meet both requirements.