Comment by ketzu
14 hours ago
"zero sized objects don't have identity" actually would answer my question and is a really interesting factoid, thanks!
14 hours ago
"zero sized objects don't have identity" actually would answer my question and is a really interesting factoid, thanks!
This is why C++ doesn't have ZSTs, it wants all objects to have identities, the obvious way to distinguish them is by where they are in memory, but ZSTs don't have distinct addresses in memory.
I'm not a C++ expert. Why does C++ want all objects to have identities? Presumably it has some feature or something Rust doesn't have that requires this?
It's pretty deeply tied into C++'s object lifetime mechanics, which rely on storage being available and reserved for the use of that object's lifetime. If multiple objects with valid lifetimes had a situation where one lifetime needs to end, what should happen to the other objects' lifetimes?
C++ actually did end up evolving the ability to define a zero-sized class without a unique memory address, but mostly to allow optimizations like the empty base optimization to apply in other situations where it could make sense, especially with templated or constexpr code.
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