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| use std::boxed::Box; | |
| use std::rc::Rc; | |
| use std::borrow::Borrow; | |
| use std::mem; | |
| struct BP_REF; | |
| struct BP_BOX; | |
| struct BP_OWNED; | |
| struct BP_RC; | |
| struct Ref<'a, T: 'a>(&'a T); | |
| unsafe trait BorrowPlus<Borrowed: ?Sized, TRef> | |
| : Borrow<Borrowed> + std::marker::Sized { | |
| fn borrowPlusToRC(self) -> Rc<Borrowed> | |
| where Self: BorrowPlus<Borrowed, BP_RC> | |
| { | |
| panic!("Impossible") | |
| } | |
| fn borrowPlusToOwned(self) -> Self | |
| where Self: BorrowPlus<Borrowed, BP_OWNED> | |
| { | |
| panic!("Impossible") | |
| } | |
| fn borrowPlusToBox(self) -> Box<Borrowed> | |
| where Self: BorrowPlus<Borrowed, BP_BOX> | |
| { | |
| panic!("Impossible") | |
| } | |
| } | |
| unsafe impl<Borrowed> BorrowPlus<Borrowed, BP_RC> for Rc<Borrowed> { | |
| fn borrowPlusToRC(self) -> Rc<Borrowed> { | |
| self | |
| } | |
| } | |
| unsafe impl<'a, Borrowed> BorrowPlus<Borrowed, BP_REF> for &'a Borrowed {} | |
| unsafe impl<Borrowed> BorrowPlus<Borrowed, BP_BOX> for Box<Borrowed> { | |
| fn borrowPlusToBox(self) -> Box<Borrowed> { | |
| self | |
| } | |
| } | |
| unsafe impl<Borrowed> BorrowPlus<Borrowed, BP_OWNED> for Borrowed { | |
| fn borrowPlusToOwned(self) -> Borrowed { | |
| self | |
| } | |
| } | |
| fn asRc<T, BP: BorrowPlus<T, BP_RC>>(x: BP) -> Rc<T> { | |
| x.borrowPlusToRC() | |
| } | |
| fn asBox<T, BP: BorrowPlus<T, BP_BOX>>(x: BP) -> Box<T> { | |
| x.borrowPlusToBox() | |
| } | |
| fn main() { | |
| let x = 3; | |
| let y = &x; | |
| // let z = asRc(y); //should not compile | |
| let x = 3; | |
| let y = Rc::new(x); | |
| let z = asRc(y); | |
| () | |
| } |
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