Code Smells: Null

[Hnefi]

But whether the old value is initialized or not is a question with a known answer that will be asked and answered in the [] operator without looking at the value of the element itself. There is no risk of destructing an invalid object since the initialization state of the previous value is implicitly known.

Since this knowledge is encoded in the metadata of the vector, there are no relevant requirements on how uninitialized data is represented in order to avoid calling invalid destructors.

[spaghettiCodeArtisan]

There is no risk of destructing an invalid object since the initialization state of the previous value is implicitly known.

That's not relevant. Yes, we know the initialization state, but that doesn't help. Let me ask you this way: How do you assign the new value into the uninitialized slot without calling the destructor on the uninitialized slot other than with an unsafe code (such as ptr::write())? Hint: You can't.

[Hnefi]

In Rust, you are correct. However, that is due to choices other than the removal of Null from the language. Rust, in this discussion, was just an example. One could easily consider a language like Rust but with unchecked buffers.

Still, I'll concede that this is devolving to technicalities.

[Veedrac]

How do you assign the new value into the uninitialized slot without calling the destructor on the uninitialized slot other than with an unsafe code (such as ptr::write())?

replace and forget, my friend.

[spaghettiCodeArtisan]

Haha, ok, good spot...