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use std::ops::Deref; struct RefCountAndT<T> { ref_count: usize, obj: T, } struct Rc<T> { ref_count_and_t: *mut RefCountAndT<T>, } impl <T> Rc<T> { pub fn new(obj: T) -> Self { //Move 'obj' onto the heap into a new RefCountAndT instance. We can use Box for this, just temporarily! let ref_count_and_t = Box::new(RefCountAndT { ref_count: 1, obj, }); //Now we *leak* the box to obtain the raw pointer! Box::leak returns a mutable *borrow*... let leaked : &mut RefCountAndT<T> = Box::leak(ref_count_and_t); //...but we want a *pointer*. Luckily, we can cast one into the other. This does NOT require unsafe code, //only *using* the pointer is unsafe (because it can be null)! let leaked_ptr : *mut RefCountAndT<T> = leaked; Self { ref_count_and_t: leaked_ptr, } } pub fn get(&self) -> &T { unsafe { &self.ref_count_and_t.as_ref().unwrap().obj } } pub fn get_mut(&mut self) -> &mut T { unsafe { &mut self.ref_count_and_t.as_mut().unwrap().obj } } } impl <T> Drop for Rc<T> { fn drop(&mut self) { unsafe { let ref_count_and_t = self.ref_count_and_t.as_mut().unwrap(); ref_count_and_t.ref_count -= 1; if ref_count_and_t.ref_count == 0 { let _as_box = Box::from_raw(self.ref_count_and_t); } } } } impl <T> Clone for Rc<T> { fn clone(&self) -> Self { unsafe { let ref_count_and_t = self.ref_count_and_t.as_mut().unwrap(); ref_count_and_t.ref_count += 1; } Self { ref_count_and_t: self.ref_count_and_t } } } impl <T> Deref for Rc<T> { type Target = T; fn deref(&self) -> &Self::Target { self.get() } } struct Test {} impl Test { pub fn foo(&self) { println!("Test -> foo"); } } pub fn main() { let mut rc1 = Rc::new(Test{}); let mut rc2 = rc1.clone(); let mut1 = rc1.get_mut(); let mut2 = rc2.get_mut(); mut1.foo(); mut2.foo(); }
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