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#![allow(dead_code)] //! Module defining DependentRc, a wrapper around the Rc type. //! //! This module both defines the `DependentRc` struct, as well as the corresponding `to_view!` macro, which can be used to obtain views from an instance of `DependentRc`. //! use super::push_ref; use std::rc::Rc; use std::convert::*; use std::any::Any; use std::mem::transmute; use std::ops::{Deref, DerefMut}; /// Macro for obtaining views from DependentRc /// /// # Error /// It is a compile time error to use this macro to produce a view for a trait that the underlying struct does not implement. /// /// # Examples /// /// ``` /// # use std::rc::Weak; /// # #[macro_use] extern crate dependent_view; /// # use dependent_view::rc::DependentRc; /// struct ExampleStruct { /// // arbitrary fields /// # id: usize /// } /// trait ExampleTrait { /// fn example_method(&self); /// } /// # impl ExampleStruct { fn new() -> Self { ExampleStruct {id: 0}}} /// impl ExampleTrait for ExampleStruct { /// # fn example_method(&self) { /// // some implementation... /// # println!("id: {:?}", self.id); /// # } /// } /// # fn main() { /// let mut item : DependentRc<ExampleStruct> = DependentRc::new(ExampleStruct::new()); /// let view : Weak<ExampleTrait> = to_view!(item); /// # } /// ``` #[macro_export] macro_rules! to_view { ($dep:tt) => { (unsafe { $dep.into_view_internal::<_, _,_, _, _>(|item| item.clone() as ::std::rc::Rc<_>, |item| ::std::rc::Rc::downgrade(item), |item| unsafe { ::std::mem::transmute(item) })}); } } /// `DependentRc<T>` is a simple wrapper around the `Rc<T>` type, imbuing it with the capability to provide "views" (`Weak<Trait>`) of non-owned structs to separate components of a system. /// /// Internally, it does this by retaining an `Rc<Trait>` for each view you make - thus when the /// `DependentRc` is dropped, all of the weak references are automatically invalidated. pub struct DependentRc<T> { item: Rc<T>, dependants: Vec<Rc<Any>> } impl<T> DependentRc<T> { /// Constructs a `DependentRc` by wrapping an underlying type pub fn new(item: T) -> DependentRc<T> { DependentRc { item: Rc::new(item), dependants: Vec::new() } } /// internal hidden function used to produce a Weak reference /// # Warn /// This function should only be called through the `to_view!` macro. It is not intended for direct use. /// # Remarks /// This struct works by cloning the underlying Rc, using the fact that when cloning, it is possible /// to upcast an `Rc<Concrete>` to an `Rc<Trait>`. /// From this point, the `Rc<Trait>` is transmuted into an `Rc<Any>`. While this is an unsafe, /// unchecked cast, we just want to keep the on Drop functionality of `Rc<Any>` and don't provide /// any ways to use the trait, so it shouldn't be a problem #[doc(hidden)] pub unsafe fn into_view_internal<X,Y,G,F, H>(&mut self, conversion: F, downgrade: G, to_any: H) -> Y where F : FnOnce(&Rc<T>) -> X, G : FnOnce(&X) -> Y, H : FnOnce(X) -> Rc<Any> { let reference : X = conversion(&self.item); let reference : Rc<Any> = to_any(reference); let reference : &Rc<Any> = push_ref(&mut self.dependants, reference); let reference : &X = transmute(reference); downgrade(reference) } } impl<T> Deref for DependentRc<T> { type Target = Rc<T>; fn deref(&self) -> &Rc<T> { &self.item } } impl<T> DerefMut for DependentRc<T> { fn deref_mut(&mut self) -> &mut Rc<T> { &mut self.item } } /// Returns a reference to the underlying `Rc` struct impl<T> AsRef<Rc<T>> for DependentRc<T> { fn as_ref(&self) -> &Rc<T> { &self.item } } /// Returns a mutable reference to the underlying `Rc` struct impl<T> AsMut<Rc<T>> for DependentRc<T> { fn as_mut(&mut self) -> &mut Rc<T> { &mut self.item } } /// Constructs a DependentRc from an `Rc`, imbuing it with the capability to produce views. impl <T> From<Rc<T>> for DependentRc<T> { fn from(item: Rc<T>) -> DependentRc<T> { DependentRc { item, dependants: Vec::new() } } } /// Unwraps the `DependentRc`, returning it's internal `Rc` /// /// Note: This will invalidate all `Weak<Trait>` views you have constructed from this object. impl <T> Into<Rc<T>> for DependentRc<T> { fn into(self) -> Rc<T> { self.item } }