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#![deny(missing_docs)] //! Hashable wrappers for reference countings. //! //! Provides hashable wrappers for //! [`Rc<T>`](https://doc.rust-lang.org/std/rc/struct.Rc.html) and //! [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html) //! references with the types [`HashableRc<T>`](struct.HashableRc.html) //! and [`HashableWeak<T>`](struct.HashableWeak.html), respectively. //! This allows use of both strong and weak reference countings in //! hash-based data structures, such as //! [`HashMap`](https://doc.rust-lang.org/std/collections/struct.HashMap.html) //! or //! [`HashSet`](https://doc.rust-lang.org/std/collections/struct.HashSet.html). //! //! # Quick Start //! //! The most common use cases are wrapping //! [`Rc<T>`](https://doc.rust-lang.org/std/rc/struct.Rc.html) or //! [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html) in //! [`HashableRc<T>`](struct.HashableRc.html) or //! [`HashableWeak<T>`](struct.HashableWeak.html) respectively to be //! contained in a hash-based container. An example of using both types //! as keys in a //! [`HashMap`](https://doc.rust-lang.org/std/collections/struct.HashMap.html) //! follows. //! //! ``` //! use std::collections::HashMap; //! use std::rc::{Rc, Weak}; //! //! use hashable_rc::{HashableRc, HashableWeak}; //! //! // Create a strong reference counting for an object. //! let rc: Rc<u32> = Rc::new(42); //! //! // Use the strong reference as a key for a HashMap. //! let mut strong_map = HashMap::new(); //! strong_map.insert(HashableRc::new(rc.clone()), "foo"); //! assert_eq!(strong_map[&HashableRc::new(rc.clone())], "foo"); //! //! // Create a weak reference counting for the same object as above. //! let weak: Weak<u32> = Rc::downgrade(&rc); //! //! // Use the weak reference as a key for a HashMap. //! let mut weak_map = HashMap::new(); //! weak_map.insert(HashableWeak::new(weak.clone()), "bar"); //! assert_eq!(weak_map[&HashableWeak::new(weak.clone())], "bar"); //! ``` //! //! Insertion into other hash-based containers (such as a //! [`HashSet`](https://doc.rust-lang.org/std/collections/struct.HashSet.html)) //! follows similarly. use std::hash::{Hash, Hasher}; use std::rc::{Rc, Weak}; fn hash_rc<T, H: Hasher>(rc: Rc<T>, state: &mut H) { let raw_ptr = Rc::into_raw(rc); raw_ptr.hash(state); // Convert back to Rc to prevent memory leak. let _ = unsafe {Rc::from_raw(raw_ptr)}; } /// A hashable wrapper around the /// [`Rc<T>`](https://doc.rust-lang.org/std/rc/struct.Rc.html) type. /// /// A hash of a [`HashableRc<T>`](struct.HashableRc.html) is taken from /// the underlying pointer. Therefore, two separate objects that may be /// considered equal will, when contained in a /// [`HashableRc<T>`](struct.HashableRc.html), almost always have /// different hashed values. For example, the following holds: /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::{Hash, Hasher}; /// use std::rc::Rc; /// /// use hashable_rc::HashableRc; /// /// fn hash<H: Hash>(value: &H) -> u64 { /// let mut state = DefaultHasher::new(); /// value.hash(&mut state); /// state.finish() /// } /// /// // While the underlying values are considered equal, the hash values /// // will be different, due to being separate allocated objects with /// // different underlying pointers. /// let rc1 = Rc::new(42); /// let rc2 = Rc::new(42); /// /// // The hashes of the two reference countings are different. /// assert_ne!(hash(&HashableRc::new(rc1.clone())), /// hash(&HashableRc::new(rc2.clone()))); /// /// // Contrastingly, the hashes of clone reference countings pointing to /// // the same object are the equal. /// assert_eq!(hash(&HashableRc::new(rc1.clone())), /// hash(&HashableRc::new(rc1.clone()))); /// ``` /// /// Similarly, equality of [`HashableRc<T>`](struct.HashableRc.html) /// objects is done by evaluating pointer equality (using /// [`ptr_eq()`](https://doc.rust-lang.org/std/rc/struct.Rc.html#method.ptr_eq)). /// The equality is not from the value itself, but from the pointer. /// /// ``` /// use std::rc::Rc; /// /// use hashable_rc::HashableRc; /// /// // Again, the values contained are equal, but the underlying pointers /// // are different. /// let rc1 = Rc::new(42); /// let rc2 = Rc::new(42); /// /// // Therefore, two HashableRc wrappers containing these reference /// // counters are not equal. /// assert_ne!(HashableRc::new(rc1.clone()), /// HashableRc::new(rc2.clone())); /// /// // But HashableRc holding the same underlying object are equal. /// assert_eq!(HashableRc::new(rc1.clone()), /// HashableRc::new(rc1.clone())); /// ``` #[derive(Debug, Eq)] pub struct HashableRc<T> { value: Rc<T>, } impl <T> HashableRc<T> { /// Constructs a new [`HashableRc<T>`](struct.HashableRc.html) /// wrapping an /// [`Rc<T>`](https://doc.rust-lang.org/std/rc/struct.Rc.html). pub fn new(value: Rc<T>) -> Self { HashableRc {value} } /// Returns a clone of the wrapped `Rc<T>` without consuming `self`. pub fn get_cloned(&self) -> Rc<T> { self.value.clone() } } impl <T> Hash for HashableRc<T> { /// Generate a hash value for the /// [`HashableRc<T>`](struct.HashableRc.html). /// /// This hash value is based on the underlying pointer. Two unique /// objects will most likely have different hashes, even if their /// values are the same. fn hash<H>(&self, state: &mut H) where H: Hasher { hash_rc(self.value.clone(), state); } } impl <T> PartialEq for HashableRc<T> { /// Equality for two [`HashableRc<T>`](struct.HashableRc.html) /// objects. /// /// Equality is determined by pointer equality, rather than value /// equality. Objects are only considered equal if they point to /// the same object. fn eq(&self, other: &Self) -> bool { Rc::ptr_eq(&self.value, &other.value) } } /// A hashable wrapper around the /// [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html) /// type. /// /// A hash of a [`HashableWeak<T>`](struct.HashableWeak.html) is taken /// from the underlying pointer. Therefore, two separate objects that /// may be considered equal will, when contained in a /// [`HashableWeak<T>`](struct.HashableWeak.html), almost always have /// different hashed values. For example, the following holds: /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::{Hash, Hasher}; /// use std::rc::Rc; /// /// use hashable_rc::HashableWeak; /// /// fn hash<H: Hash>(value: &H) -> u64 { /// let mut state = DefaultHasher::new(); /// value.hash(&mut state); /// state.finish() /// } /// /// // While the underlying values are considered equal, the hash values /// // will be different, due to being separate allocated objects with /// // different underlying pointers. /// let rc1 = Rc::new(42); /// let rc2 = Rc::new(42); /// /// // The hashes of the two reference countings are different. /// assert_ne!(hash(&HashableWeak::new(Rc::downgrade(&rc1))), /// hash(&HashableWeak::new(Rc::downgrade(&rc2)))); /// /// // Contrastingly, the hashes of clone reference countings pointing to /// // the same object are the equal. /// assert_eq!(hash(&HashableWeak::new(Rc::downgrade(&rc1))), /// hash(&HashableWeak::new(Rc::downgrade(&rc1)))); /// ``` /// /// Similarly, equality of /// [`HashableWeak<T>`](struct.HashableWeak.html) objects is done by /// evaluating pointer equality (using /// [`ptr_eq()`](https://doc.rust-lang.org/std/rc/struct.Weak.html#method.ptr_eq)). /// The equality is not from the value itself, but from the pointer. /// /// ``` /// use std::rc::Rc; /// /// use hashable_rc::HashableWeak; /// /// // Again, the values contained are equal, but the underlying pointers /// // are different. /// let rc1 = Rc::new(42); /// let rc2 = Rc::new(42); /// /// // Therefore, two HashableWeak wrappers containing these reference /// // counters are not equal. /// assert_ne!(HashableWeak::new(Rc::downgrade(&rc1)), /// HashableWeak::new(Rc::downgrade(&rc2))); /// /// // But HashableWeak holding the same underlying object are equal. /// assert_eq!(HashableWeak::new(Rc::downgrade(&rc1)), /// HashableWeak::new(Rc::downgrade(&rc1))); /// ``` /// /// Since /// [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html) is a /// weak reference, the underlying value is not guaranteed to exist. A /// [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html) that /// is empty can still be wrapped in a /// [`HashableWeak<T>`](struct.HashableWeak.html). /// /// ``` /// use std::collections::hash_map::DefaultHasher; /// use std::hash::{Hash, Hasher}; /// use std::rc::{Rc, Weak}; /// /// use hashable_rc::HashableWeak; /// /// fn hash<H: Hash>(value: &H) -> u64 { /// let mut state = DefaultHasher::new(); /// value.hash(&mut state); /// state.finish() /// } /// /// let weak: Weak<i32> = Weak::new(); /// let rc = Rc::new(0); /// /// // Hashing still works for a HashableWeak pointing to no value. It will /// // hash differently than HashableWeak objects containing values, and /// // will hash the same as other empty HashableWeak objects. /// assert_ne!(hash(&HashableWeak::new(weak.clone())), /// hash(&HashableWeak::new(Rc::downgrade(&rc)))); /// assert_eq!(hash(&HashableWeak::new(weak.clone())), /// hash(&HashableWeak::new(weak.clone()))); /// /// // Empty HashableWeak objects are also not equal to assigned /// // HashableWeak objects, while being equal to other empty HashableWeak /// // objects. /// assert_ne!(HashableWeak::new(weak.clone()), /// HashableWeak::new(Rc::downgrade(&rc))); /// assert_eq!(HashableWeak::new(weak.clone()), /// HashableWeak::new(weak.clone())); /// ``` #[derive(Debug)] pub struct HashableWeak<T> { value: Weak<T>, } impl <T> HashableWeak<T> { /// Constructs a new [`HashableWeak<T>`](struct.HashableWeak.html) /// wrapping a /// [`Weak<T>`](https://doc.rust-lang.org/std/rc/struct.Weak.html). pub fn new(value: Weak<T>) -> Self { HashableWeak {value} } } impl <T> Hash for HashableWeak<T> { /// Generate a hash value for the /// [`HashableWeak<T>`](struct.HashableWeak.html). /// /// This hash value is based on the underlying pointer. Two unique /// objects will most likely have different hashes, even if their /// values are the same. /// /// If no value is pointed to, the Hasher state remains unaltered. fn hash<H>(&self, state: &mut H) where H: Hasher { let upgraded_weak: Option<Rc<T>> = self.value.clone().upgrade(); match upgraded_weak { None => {} Some(rc) => { hash_rc(rc, state); } } } } impl <T> PartialEq for HashableWeak<T> { /// Equality for two [`HashableWeak<T>`](struct.HashableWeak.html) /// objects. /// /// Equality is determined by pointer equality, rather than value /// equality. Objects are only considered equal if they point to /// the same object (or if both point to no object). fn eq(&self, other: &Self) -> bool { Weak::ptr_eq(&self.value, &other.value) } } impl <T> Eq for HashableWeak<T> {} #[cfg(test)] mod tests { use crate::{HashableRc, HashableWeak}; use std::collections::hash_map::DefaultHasher; use std::hash::{Hash, Hasher}; use std::rc::{Rc, Weak}; fn hash<H: Hash>(value: &H) -> u64 { let mut state = DefaultHasher::new(); value.hash(&mut state); state.finish() } #[test] fn test_hashable_rc_hash() { let rc1 = Rc::new(42); let rc2 = Rc::new(42); assert_ne!(hash(&HashableRc::new(rc1.clone())), hash(&HashableRc::new(rc2.clone()))); assert_eq!(hash(&HashableRc::new(rc1.clone())), hash(&HashableRc::new(rc1.clone()))); } #[test] fn test_hashable_rc_eq() { let rc1 = Rc::new(42); let rc2 = Rc::new(42); assert_ne!(HashableRc::new(rc1.clone()), HashableRc::new(rc2.clone())); assert_eq!(HashableRc::new(rc1.clone()), HashableRc::new(rc1.clone())); } #[test] fn test_hashable_rc_get_clone() { let rc1 = Rc::new(42); let rc2 = Rc::new(42); let rc1_hashable = HashableRc::new(rc1.clone()); assert_eq!(rc1_hashable.get_cloned(), rc1); assert_eq!(rc1_hashable.get_cloned(), rc2); // Round trip follows from above, but included for completeness. assert_eq!(HashableRc::new(rc1_hashable.get_cloned()), rc1_hashable); // Round trip the other direction. assert_eq!(*rc1_hashable.get_cloned(), 42); } #[test] fn test_hashable_rc_hash_does_not_memory_leak() { let rc = Rc::new(42); hash(&HashableRc::new(rc.clone())); assert_eq!(Rc::strong_count(&rc), 1); assert_eq!(Rc::weak_count(&rc), 0); } #[test] fn test_hashable_weak_hash() { let rc1 = Rc::new(42); let rc2 = Rc::new(42); assert_ne!(hash(&HashableWeak::new(Rc::downgrade(&rc1))), hash(&HashableWeak::new(Rc::downgrade(&rc2)))); assert_eq!(hash(&HashableWeak::new(Rc::downgrade(&rc1))), hash(&HashableWeak::new(Rc::downgrade(&rc1)))); } #[test] fn test_hashable_weak_eq() { let rc1 = Rc::new(42); let rc2 = Rc::new(42); assert_ne!(HashableWeak::new(Rc::downgrade(&rc1)), HashableWeak::new(Rc::downgrade(&rc2))); assert_eq!(HashableWeak::new(Rc::downgrade(&rc1)), HashableWeak::new(Rc::downgrade(&rc1))); } #[test] fn test_hashable_weak_hash_does_not_memory_leak() { let rc = Rc::new(42); let weak = Rc::downgrade(&rc); hash(&HashableWeak::new(weak.clone())); assert_eq!(Rc::strong_count(&rc), 1); assert_eq!(Rc::weak_count(&rc), 1); } #[test] fn test_hashable_weak_hash_no_value() { // Weak is an empty weak reference. let weak: Weak<i32> = Weak::new(); let rc = Rc::new(0); assert_ne!(hash(&HashableWeak::new(weak.clone())), hash(&HashableWeak::new(Rc::downgrade(&rc)))); assert_eq!(hash(&HashableWeak::new(weak.clone())), hash(&HashableWeak::new(weak.clone()))); } #[test] fn test_hashable_weak_eq_no_value() { // Weak is an empty weak reference. let weak: Weak<i32> = Weak::new(); let rc = Rc::new(0); assert_ne!(HashableWeak::new(weak.clone()), HashableWeak::new(Rc::downgrade(&rc))); assert_eq!(HashableWeak::new(weak.clone()), HashableWeak::new(weak.clone())); } }