You could argue that some languages distinguish raw memory from actual objects and even when reusing memory you would still go through an initialization phase (for example placement new in C++) that would take care of putting the object into a known default state.

This statement is incorrect. They are using an arena allocator, and there is no way for it to know if it is reusing one of the elements or using that element for the first time. To do this in Rust you would probably be using the MaybeUninit type: https://doc.rust-lang.org/std/mem/union.MaybeUninit.html

However, you are partly correct. In Rust, when using the MaybeUninit type, it is still possible to partially initialize an object and then return it as if it were fully initialized without hitting a compile error. https://doc.rust-lang.org/std/mem/union.MaybeUninit.html#ini...

If you do the whole struct at once, rather than one field at a time, then the compiler still has your back:

    let foo = unsafe {
      let mut uninit: MaybeUninit<Foo> = MaybeUninit::uninit();
      uninit.write(Foo {
        name: "Bob".to_string(),
        list: vec![0, 1, 2]
      })
    }