Armanriazi•锈•图•设计•内•可变性

armanriazi•锈•图•设计•内•可变性

*o.into_mut() += 2;// About ~ like borrow_mut in RC type both of them called interior mutability pattern(Mutably the wrap value).
Interior mutability is a design pattern in Rust that allows you to mutate data even when there are immutable references to that data; normally, this action is disallowed by the borrowing rules. To mutate data, the pattern uses unsafe code inside a data structure to bend Rust’s usual rules that govern mutation and borrowing. 
RefCell<T> type that follows the interior mutability pattern.
The RefCell<T> type is useful when you’re sure your code follows the borrowing rules but the compiler is unable to understand and guarantee that.