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Copy constructors that modify the input param cannot be translated as Clone #613
Description
We translate copy constructors using the Clone trait. Clone receives an immutable reference. C++ allows copy constructors to receive a mutable reference T(T&).
We cannot express T(T&) using the Clone trait. Our current solutions mistranslate this case. Unsafe translates as
impl Clone for T {
fn clone(&self) {
// the cast is UB if copy_from actually modifies self
T::copy_from(&self as *const T as *mut T)
}
}Refcount translates as:
impl Clone for T {
fn clone(&self) -> Self {
let __src: Value<T> = Rc::new(RefCell::new(T { a: self.a.clone(), ... }));
// Any modification on self is lost because __src is a temporary
T::copy_from(__src.as_pointer())
}
}Also the refcount translation is slow, see #510
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