17-3 rationale for using Option for State is still unclear

• I have searched open and closed issues and pull requests for duplicates, using these search terms:

  • self.state.request_review

• I have checked the latest main branch to see if this has already been fixed, in this file:

  • https://github.com/rust-lang/book/blob/main/src/ch17-03-oo-design-patterns.md

URL to the section(s) of the book with this problem:
https://doc.rust-lang.org/book/ch17-03-oo-design-patterns.html#requesting-a-review-of-the-post-changes-its-state

Description of the problem:
The following sentence is still very confusing:

We need to set state to None temporarily rather than setting it directly with code like self.state = self.state.request_review(); to get ownership of the state value. This ensures Post can’t use the old state value after we’ve transformed it into a new state.

First, "We need" implies that self.state = self.state.request_review() gives the incorrect result. However, it actually gives the correct result; from https://github.com/rust-lang/book/issues/837, the intent here is to make the code less error-prone in case that line is later commented out.

Additionally. "This ensures Post can’t use the old state value after we’ve transformed it into a new state." seems misleading too. Post already cannot use the old state value, since the self parameter is moved in request_review(self: Box<Self>). This would only "ensure" if we for some reason changed the self parameter to borrow.

Suggested fix:

Please add a paragraph making it clear that the usage of Option is solely to make the code less error-prone in the face of future refactorings, and not explicitly needed for correctness.

Read src/ch17-03-oo-design-patterns.md at the section on requesting a review of the post changes its state, along with the referenced discussion in issue 837. Revise the explanation so it distinguishes correctness from protection against future refactoring, then verify the rendered book section clearly reflects that rationale.