Comment by tialaramex

std::unique_ptr<T> is almost exactly Option<Box<T>>

The Option is important, Rust's Box<T> is always a boxed T, but std::unique_ptr<T> might not be a boxed T, it might be "disengaged" and there isn't a T

C++ move operations are thus closest to Rust's core::mem::take function, they not only move something, they also need to always replace it with some empty default state, in Rust's case specifically Default::default. Box<T> may not implement Default, but Option does so unconditionally, because its default is always just None.

You may find when converting some code that you didn't want Option<Box<T>> but only Box<T> because in fact you always have a boxed T here - it's never disengaged, and if you do that then Rust's type system has helped in a small way to clarify your code so that's nice.