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#![deny(missing_docs)] //! A crate with a few single-typed arenas that work exclusively with indexes. //! The indexes are sized with the arena. This can reduce memory footprint when //! changing pointers to indices e.g. on 64-bit systems. //! //! The arenas use a variant of "branded indices": The indices contain a type //! tag that binds them to their respective arena so you cannot mix up two //! arenas by accident. Unlike the [indexing](https://crates.io/crates/indexing) //! crate, this implements the type tags as actual unique types. This has the //! downside of not being able to `Sync` or `Send` arenas or indices, but on the //! other hand, we can store indices within objects that we put into the arena, //! which is a boon to things like graph data structures. //! //! A word of warning: The soundness of this isn't proven, and it may well be //! possible to use the macros provided in this crate to create undefined //! behavior. For simple use cases, you should be pretty safe. //! //! Use the `in_arena` and similar methods to run code within the scope of an //! arena: //! //! # Examples //! //! ```rust //!# use compact_arena::in_arena; //! in_arena!(arena, { //! let idx = arena.add(1usize); //! assert_eq!(1, arena[idx]); //! }); //! ``` //! //! You can use `in_sized_arena` to change the initial size of the backing //! memory: //! //! ```rust //!# #[allow(dead_code)] //!# use compact_arena::in_arena; //! in_arena!(arena / 1, { //! .. //!# ; arena.add(1usize); //! }); //! ``` //! //! You can nest calls to work with multiple arenas: //! //! ```rust //!# #[allow(dead_code)] //!# use compact_arena::in_arena; //! in_arena!(a / 1, { //! in_arena!(b / 1, { //! .. //!# ; a.add(1u32); b.add(1u32); //! }) //! }); //! ``` //! //! The compiler gives you a type error if you mix up arenas: //! //! ```rust,compile_fail //!# use compact_arena::in_arena; //! in_arena!(a / 1, { //! in_arena!(b / 1, { //! let i = a.add(1usize); //! let _ = b[i]; //! }) //! }); //! ``` use core::ops::{Index, IndexMut}; use core::marker::PhantomData; /// An index into the arena. You will not directly use this type, but one of /// the aliases this crate provides (`Idx32`, `Idx16` or `Idx8`). /// /// The only way to get an index into an arena is to `add` a value to it. With /// an `Idx` you can index or mutably index into the arena to observe or mutate /// the value. #[derive(PartialOrd, PartialEq, Eq)] pub struct Idx<I: Copy + Clone, B> { index: I, tag: PhantomData<B>, } impl<I: Copy + Clone, B> Copy for Idx<I, B> { } impl<I: Copy + Clone, B> Clone for Idx<I, B> { fn clone(&self) -> Self { *self } } /// The index type for a small arena is 32 bits large. You will usually get the /// index from the arena and use it by indexing, e.g. `arena[index]`. /// /// # Examples /// /// ```rust ///# use core::mem::size_of; ///# use compact_arena::Idx32; /// assert_eq!(size_of::<Idx32<String>>(), size_of::<u32>()); /// ``` pub type Idx32<B> = Idx<u32, B>; /// The index type for a tiny arena is 16 bits large. You will usually get the /// index from the arena and use it by indexing, e.g. `arena[index]`. /// /// # Examples: /// /// ```rust ///# use compact_arena::Idx16; ///# use core::mem::size_of; /// assert_eq!(size_of::<Idx16<usize>>(), size_of::<u16>()); /// ``` pub type Idx16<B> = Idx<u16, B>; /// The index type for a nano arena is 8 bits large. You will usually get the /// index from the arena and use it by indexing, e.g. `arena[index]`. /// /// # Examples: /// /// ```rust ///# use compact_arena::Idx8; ///# use core::mem::size_of; /// assert_eq!(size_of::<Idx8<i128>>(), size_of::<u8>()); /// ``` pub type Idx8<B> = Idx<u8, B>; /// A "Small" arena based on a resizable slice (i.e. a `Vec`) that can be /// indexed with 32-bit `Idx32`s. This can help reduce memory overhead when /// using many pointer-heavy objects on 64-bit systems. /// /// You will usually use this type by calling `in_arena` or similar functions. pub struct SmallArena<T, B> { tag: PhantomData<B>, // TODO: Use a custom structure, forbid resizing over 2G items data: Vec<T>, } /// Run code using an arena. The indirection through the macro is required /// to safely bind the indices to the arena. The macro takes an identifier that /// will be bound to the `&mut Arena<_, _>` and an expression that will be /// executed within a block where the arena is instantiated. The arena will be /// dropped afterwards. /// /// # Examples /// /// ``` ///# use compact_arena::in_arena; /// assert_eq!(in_arena!(arena, { /// let half = arena.add(21); /// arena[half] + arena[half] /// }), 42); /// ``` /// /// You can also specify an initial size after the arena identifier: /// /// ``` ///# #[allow(dead_code)] ///# use compact_arena::in_arena; /// in_arena!(arena / 65536, { ///# arena.add(2usize); /// .. /// }); /// ``` #[macro_export] macro_rules! in_arena { ($arena:ident, $e:expr) => { in_arena!($arena / 1024*1024, $e) }; ($arena:ident / $cap:expr, $e:expr) => { { #[derive(Copy, Clone)] struct Tag; let mut x = unsafe { compact_arena::SmallArena::new(Tag, $cap) }; { let $arena = &mut x; $e } } }; } /// Run code using a tiny arena. The indirection through this macro is /// required to bind the indices to the arena. /// /// # Examples /// /// ```rust ///# use compact_arena::in_tiny_arena; /// in_tiny_arena!(arena, { /// let idx = arena.add(1usize); /// assert_eq!(1, arena[idx]); /// }); /// ``` #[macro_export] macro_rules! in_tiny_arena { ($arena:ident, $e:expr) => { { #[derive(Copy, Clone)] struct Tag; let mut x = unsafe { compact_arena::TinyArena::new(Tag) }; { let $arena = &mut x; $e } } }; } /// Run code using a nano arena. The indirection through the macro is /// required to bind the indices to the arena. /// /// # Examples /// /// ```rust ///# use compact_arena::in_nano_arena; /// in_nano_arena!(arena, { /// let idx = arena.add(1usize); /// assert_eq!(1, arena[idx]); /// }); /// ``` #[macro_export] macro_rules! in_nano_arena { ($arena:ident, $e:expr) => { { #[derive(Copy, Clone)] struct Tag; let mut x = unsafe { compact_arena::NanoArena::new(Tag) }; { let $arena = &mut x; $e } } }; } impl<T, B> SmallArena<T, B> { /// create a new SmallArena. Don't do this manually. Use the /// [`in_arena`] macro instead. /// /// # Safety /// /// The whole tagged indexing trick relies on the `B` type you give to this /// constructor. You must never use this type in another arena, lest you /// might be able to mix up the indices of the two, which could lead to /// out of bounds access and thus **Undefined Behavior**! pub unsafe fn new(_: B, capacity: usize) -> SmallArena<T, B> { SmallArena { tag: PhantomData, data: Vec::with_capacity(capacity), } } /// Add an item to the arena, get an index back. #[inline] pub fn add(&mut self, item: T) -> Idx32<B> { let i = self.data.len() as u32; self.data.push(item); Idx { index: i, tag: self.tag } } } impl<B, T> Index<Idx32<B>> for SmallArena<T, B> { type Output = T; /// Gets an immutable reference to the value at this index. #[inline] fn index(&self, i: Idx32<B>) -> &T { debug_assert!((i.index as usize) < self.data.len()); unsafe { &self.data.get_unchecked(i.index as usize) } } } impl<B, T> IndexMut<Idx32<B>> for SmallArena<T, B> { /// Gets a mutable reference to the value at this index. #[inline] fn index_mut(&mut self, i: Idx32<B>) -> &mut T { debug_assert!((i.index as usize) < self.data.len()); unsafe { self.data.get_unchecked_mut(i.index as usize) } } } const TINY_ARENA_ITEMS: usize = 65535; const NANO_ARENA_ITEMS: usize = 255; pub use tiny_arena::{TinyArena, NanoArena}; #[cfg(not(feature = "uninit"))] mod tiny_arena { use crate::{Idx16, Idx8, TINY_ARENA_ITEMS, NANO_ARENA_ITEMS}; use core::ops::{Index, IndexMut}; use core::marker::PhantomData; /// A "tiny" arena containing <64K elements. This variant only works with /// types implementing `Default`. /// /// You will likely use this via the `in_tiny_arena` function. pub struct TinyArena<T, B> { tag: PhantomData<B>, len: u16, data: [T; TINY_ARENA_ITEMS], } impl<T: Copy + Clone + Default, B> TinyArena<T, B> { /// create a new TinyArena. Don't do this manually. Use the /// [`in_tiny_arena`] macro instead. /// /// # Safety /// /// The whole tagged indexing trick relies on the `B` type you give to /// this constructor. You must never use this type in another arena, /// lest you might be able to mix up the indices of the two, which /// could lead to out of bounds access and thus **Undefined Behavior**! pub unsafe fn new(_: B) -> TinyArena<T, B> { TinyArena { tag: PhantomData, data: [Default::default(); TINY_ARENA_ITEMS], len: 0 } } /// Add an item to the arena, get an index back pub fn add(&mut self, item: T) -> Idx16<B> { let i = self.len; assert!((i as usize) < TINY_ARENA_ITEMS); self.data[i as usize] = item; self.len += 1; Idx16 { tag: self.tag, index: i } } } impl<T, B> Index<Idx16<B>> for TinyArena<T, B> { type Output = T; fn index(&self, i: Idx16<B>) -> &T { debug_assert!(i.index < self.len); &self.data[i.index as usize] } } impl<T, B> IndexMut<Idx16<B>> for TinyArena<T, B> { fn index_mut(&mut self, i: Idx16<B>) -> &mut T { debug_assert!(i.index < self.len); &mut self.data[i.index as usize] } } /// A "nano" arena containing 255 elements. This variant only works with /// types implementing `Default`. /// /// You will likely use this via the `in_nano_arena` function. pub struct NanoArena<T, B> { tag: PhantomData<B>, len: u8, data: [T; NANO_ARENA_ITEMS], } impl<T: Default + Copy, B> NanoArena<T, B> { /// create a new NanoArena. Don't do this manually. Use the /// [`in_nano_arena`] macro instead. /// /// # Safety /// /// The whole tagged indexing trick relies on the `B` type you give to /// this constructor. You must never use this type in another arena, /// lest you might be able to mix up the indices of the two, which /// could lead to out of bounds access and thus **Undefined Behavior**! pub unsafe fn new(_: B) -> NanoArena<T, B> { NanoArena { tag: PhantomData, data: [Default::default(); NANO_ARENA_ITEMS], len: 0 } } /// Add an item to the arena, get an index back pub fn add(&mut self, item: T) -> Idx8<B> { let i = self.len; assert!((i as usize) < NANO_ARENA_ITEMS); self.data[i as usize] = item; self.len += 1; Idx8 { tag: self.tag, index: i } } } impl<T, B> Index<Idx8<B>> for NanoArena<T, B> { type Output = T; fn index(&self, i: Idx8<B>) -> &T { debug_assert!(i.index < self.len); &self.data[i.index as usize] } } impl<T, B> IndexMut<Idx8<B>> for NanoArena<T, B> { fn index_mut(&mut self, i: Idx8<B>) -> &mut T { debug_assert!(i.index < self.len); &mut self.data[i.index as usize] } } } #[cfg(feature = "uninit")] mod tiny_arena { use crate::{Idx16, Idx8, TINY_ARENA_ITEMS, NANO_ARENA_ITEMS}; use core::marker::PhantomData; use core::mem::{self, ManuallyDrop}; use core::ops::{Index, IndexMut}; /// A "tiny" arena containing <64K elements. pub struct TinyArena<T, B> { tag: PhantomData<B>, len: u16, data: [ManuallyDrop<T>; TINY_ARENA_ITEMS], } impl<T, B> TinyArena<T, B> { /// create a new TinyArena pub unsafe fn new(_: B) -> TinyArena<T, B> { TinyArena { tag: PhantomData, data: mem::uninitialized(), len: 0 } } /// Add an item to the arena, get an index back pub fn add(&mut self, item: T) -> Idx16<B> { let i = self.len; self.data[i as usize] = ManuallyDrop::new(item); self.len += 1; Idx16 { tag: self.tag, index: i } } /// dropping the arena drops all values pub fn drop(&mut self) { for i in 0..self.len as usize { unsafe { ManuallyDrop::drop(&mut self.data[i]) }; } self.len = 0; } } impl<T, B> Index<Idx16<B>> for TinyArena<T, B> { type Output = T; fn index(&self, i: Idx16<B>) -> &T { &self.data[i.index as usize] } } impl<T, B> IndexMut<Idx16<B>> for TinyArena<T, B> { fn index_mut(&mut self, i: Idx16<B>) -> &mut T { &mut self.data[i.index as usize] } } // nano arena /// A "nano" arena containing up to 255 elements. pub struct NanoArena<T, B> { tag: PhantomData<B>, len: u8, data: [ManuallyDrop<T>; NANO_ARENA_ITEMS], } impl<T, B> NanoArena<T, B> { /// create a new NanoArena. Don't do this manually. Use the /// [`in_nano_arena`] macro instead. /// /// # Safety /// /// The whole tagged indexing trick relies on the `B` type you give to /// this constructor. You must never use this type in another arena, /// lest you might be able to mix up the indices of the two, which /// could lead to out of bounds access and thus **Undefined Behavior**! pub unsafe fn new(_: B) -> NanoArena<T, B> { NanoArena { tag: PhantomData, data: mem::uninitialized(), len: 0, } } /// Add an item to the arena, get an index back pub fn add(&mut self, item: T) -> Idx8<B> { let i = self.len; self.data[i as usize] = ManuallyDrop::new(item); self.len += 1; Idx8 { tag: self.tag, index: i } } /// dropping the arena drops all values pub fn drop(&mut self) { for i in 0..self.len as usize { unsafe { ManuallyDrop::drop(&mut self.data[i]) }; } self.len = 0; } } impl<T, B> Index<Idx8<B>> for NanoArena<T, B> { type Output = T; /// Gets an immutable reference to the value at this index fn index(&self, i: Idx8<B>) -> &T { &self.data[i.index as usize] } } impl<T, B> IndexMut<Idx8<B>> for NanoArena<T, B> { /// Gets a mutable reference to the value at this index fn index_mut(&mut self, i: Idx8<B>) -> &mut T { &mut self.data[i.index as usize] } } }