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// String internment
//
// Copyright (C) 2014-2020 Ryan Specialty Group, LLC.
//
// This file is part of TAME.
//
// This program is free software: you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// This program is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with this program. If not, see <http://www.gnu.org/licenses/>.
//! String internment system.
//!
//! Interned strings are represented by [`Symbol`],
//! created by an [`Interner`]:
//~
//! - [`ArenaInterner`] - Intern pool backed by an [arena][] for fast
//! and stable allocation.
//! - [`DefaultInterner`] - The currently recommended intern pool
//! configuration for symbol interning.
//! - [`FxArenaInterner`] - Intern pool backed by an [arena][] using the
//! [Fx Hash][fxhash] hashing algorithm.
//!
//! Interners return symbols by reference which allows for `O(1)` comparison
//! by pointer.
//!
//! [arena]: bumpalo
//!
//! ```
//! use tamer::sym::{Interner, DefaultInterner, Symbol, SymbolIndex};
//!
//! // Inputs to be interned
//! let a = "foo";
//! let b = &"foo".to_string();
//! let c = "foobar";
//! let d = &c[0..3];
//!
//! // Interners employ interior mutability and so do not need to be
//! // declared `mut`
//! let interner = DefaultInterner::new();
//!
//! let (ia, ib, ic, id) = (
//! interner.intern(a),
//! interner.intern(b),
//! interner.intern(c),
//! interner.intern(d),
//! );
//!
//! assert_eq!(ia, ib);
//! assert_eq!(ia, id);
//! assert_eq!(ib, id);
//! assert_ne!(ia, ic);
//!
//! // All interns can be cloned and clones are eq
//! assert_eq!(*ia, ia.clone());
//!
//! // Only "foo" and "foobar" are interned
//! assert_eq!(2, interner.len());
//! assert!(interner.contains("foo"));
//! assert!(interner.contains("foobar"));
//! assert!(!interner.contains("something else"));
//!
//! // Each symbol has an associated, densely-packed integer value
//! // that can be used for indexing
//! assert_eq!(SymbolIndex::from_u32(1), ia.index());
//! assert_eq!(SymbolIndex::from_u32(1), ib.index());
//! assert_eq!(SymbolIndex::from_u32(2), ic.index());
//! assert_eq!(SymbolIndex::from_u32(1), id.index());
//!
//! // Symbols can also be looked up by index.
//! assert_eq!(Some(ia), interner.index_lookup(ia.index()));
//! ```
//!
//! What Is String Interning?
//! =========================
//! _[String interning][]_ is a process by which a single copy of a string
//! is stored immutably in memory as part of a _pool_.
//! When the same string is later encountered,
//! a reference to the string in the pool is used rather than allocating a
//! new string.
//! Interned strings are typically referred to as "symbols" or "atoms".
//!
//! String comparison then amounts to comparing pointers (`O(1)`)
//! rather than having to scan the string (`O(n)`).
//! There is, however, a hashing cost of interning strings,
//! as well as looking up strings in the intern pool.
//!
//! [string interning]: https://en.wikipedia.org/wiki/String_interning
//!
//!
//! Internment Mechanism
//! ====================
//! The current [`DefaultInterner`] is [`FxArenaInterner`],
//! which is an [arena][]-allocated intern pool mapped by the
//! [Fx Hash][fxhash] hash function:
//!
//! 1. Strings are compared against the existing intern pool using a
//! [`HashMap`].
//! 2. If a string has not yet been interned:
//! - The string is copied into the arena-backed pool;
//! - A new [`Symbol`] is allocated adjacent to it in the arena holding
//! a string slice referencing the arena-allocated string; and
//! - The symbol is stored as the value in the [`HashMap`] for that key.
//! 3. Otherwise, a reference to the existing [`Symbol`] is returned.
//!
//! Since the arena provides a stable location in memory,
//! and all symbols are immutable,
//! [`ArenaInterner`] is able to safely return any number of references to
//! a single [`Symbol`],
//! bound to the lifetime of the arena itself.
//! Since the [`Symbol`] contains the string slice,
//! it also acts as a [smart pointer] for the interned string itself,
//! allowing [`Symbol`] to be used in any context where `&str` is
//! expected.
//! Dropping a [`Symbol`] does _not_ affect the underlying arena-allocated
//! data.
//!
//! [smart pointer]: https://doc.rust-lang.org/book/ch15-00-smart-pointers.html
//!
//! Each symbol also has an associated integer index value
//! (see [`Symbol::index`]),
//! which provides a dense range of values suitable for use in vectors
//! as an alternative to [`HashMap`] for mapping symbol data.
//! A [`SymbolIndex`] can be mapped back into its associated [`Symbol`]
//! using [`Interner::index_lookup`].
//!
//! Since a reference to the same [`Symbol`] is returned for each
//! [`Interner::intern`] and [`Interner::intern_soft`] call,
//! symbols can be compared by pointer in `O(1)` time.
//! Symbols also implement [`Copy`],
//! and will still compare equal to other symbols referencing the same
//! interned value by comparing the underlying string slice pointers.
//!
//! This implementation was heavily motivated by [Rustc's own internment
//! system][rustc-intern],
//! but differs in significant ways:
//!
//! - This implementation stores string references in [`Symbol`] rather
//! than relying on a global singleton [`Interner`];
//! - Consequently, associates the lifetime of interned strings with that
//! of the underlying arena rather than casting to `&'static`;
//! - Retrieves symbol values by pointer reference without requiring use
//! of [`Interner`] or a locking mechanism; and
//! - Stores [`Symbol`] objects in the arena rather than within a vector
//! indexed by [`SymbolIndex`].
//!
//!
//! Name Mangling
//! =============
//! Interners do not perform [name mangling][].
//! For future consideration,
//! see [RFC 2603][rfc-2603] and the [Itanium ABI][itanium-abi].
//!
//! [name mangling]: https://en.wikipedia.org/wiki/Name_mangling
//! [rfc-2603]: https://rust-lang.github.io/rfcs/2603-symbol-name-mangling-v2.html
//! [itanium-abi]: http://refspecs.linuxbase.org/cxxabi-1.86.html#mangling
//!
//!
//! Related Work and Further Reading
//! ================================
//! String interning is often tightly coupled with symbols (in the generic
//! sense),
//! sometimes called atoms.
//! Symbols can often be either interned,
//! and therefore compared for equivalency,
//! or _uninterned_,
//! which makes them unique even to symbols of the same name.
//! Interning may also be done automatically by a language for performance.
//! Languages listed below that allow for explicit interning may also
//! perform automatic interning as well
//! (for example, `'symbol` in Lisp and `lowercase_vars` as atoms in
//! Erlang).
//!
//! | Language | Interned | Uninterned |
//! | -------- | -------- | ---------- |
//! | [Erlang][] | [`list_to_atom`][edt] | _(None)_ |
//! | [GNU Emacs Lisp][] | [`intern`][es], [`intern-soft`][es] | [`make-symbol`][es], [`gensym`][es] |
//! | [GNU Guile][] | [`string->symbol`][gs], [`gensym`][gs] | [`make-symbol`][gu] |
//! | [JavaScript][] | [`Symbol.for`][js] | [`Symbol`][js] |
//! | [Java][] | [`intern`][jvs] | _(None)_ |
//! | [Lua][] | _(Automatic for string performance)_ | _(None)_ |
//! | [MIT/GNU Scheme][] | [`intern`][ms], [`intern-soft`][ms], [`string->symbol`][ms] | [`string->uninterned-symbol`][ms], [`generate-uninterned-symbol`][ms] |
//! | [PHP][] | _(Automatic for string [performance][pp])_ | _(None)_ |
//! | [Python][] | [`sys.intern`][pys] | _(None)_ |
//! | [R6RS Scheme][] | [`string->symbol`][r6s] | _(None)_ |
//! | [Racket][] | [`string->symbol`][rs], [`string->unreadable-symbol`][rs] | [`string->uninterned-symbol`][rs], [`gensym`][rs] |
//!
//! [gnu guile]: https://www.gnu.org/software/guile/
//! [gs]: https://www.gnu.org/software/guile/manual/html_node/Symbol-Primitives.html#Symbol-Primitives
//! [gu]: https://www.gnu.org/software/guile/manual/html_node/Symbol-Uninterned.html#Symbol-Uninterned
//! [gnu emacs lisp]: https://www.gnu.org/software/emacs/
//! [es]: https://www.gnu.org/software/emacs/manual/html_node/elisp/Creating-Symbols.html
//! [racket]: https://racket-lang.org/
//! [rs]: https://docs.racket-lang.org/reference/symbols.html
//! [r6rs scheme]: http://www.r6rs.org/
//! [r6s]: http://www.r6rs.org/final/html/r6rs/r6rs-Z-H-14.html
//! [mit/gnu scheme]: https://www.gnu.org/software/mit-scheme/
//! [ms]: https://www.gnu.org/software/mit-scheme/documentation/mit-scheme-ref/Symbols.html
//! [javascript]: https://developer.mozilla.org/en-US/docs/Web/JavaScript
//! [js]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Symbol
//! [java]: http://openjdk.java.net/
//! [jvs]: https://cr.openjdk.java.net/~iris/se/12/latestSpec/api/java.base/java/lang/String.html#intern()
//! [php]: https://www.php.net/
//! [pp]: https://wiki.php.net/rfc/performanceimprovements
//! [erlang]: https://erlang.org/
//! [edt]: http://erlang.org/doc/reference_manual/data_types.html
//! [lua]: https://www.lua.org/
//! [python]: https://www.python.org/
//! [pys]: https://docs.python.org/3/library/sys.html
//!
//! More information:
//! - Wikipedia entry on [string interning][].
//! - The [flyweight pattern][] in object-oriented programming is a type
//! of interning.
//! - [RFC 1845][rfc-1845] gives an example of string interning using
//! `Rc<str>`.
//! - Emacs directly exposes the intern pool at runtime as
//! [`obarray`][es].
//! - [`string-cache`][rust-string-cache] is a string interning system
//! for Rust developed by Mozilla for Servo.
//! - [`string-interner`][rust-string-interner] is another string
//! interning library for Rust.
//! - [Rustc interns strings as `Symbol`s][rustc-intern] using an
//! [arena allocator][rustc-arena] and avoids `Rc` by representing
//! symbols as integer values and converting them to strings using a
//! global pool and unsafe rust to cast to a `static` slice.
//! - Rustc identifies symbols by integer value encapsulated within a
//! `Symbol`.
//! - Rustc's [`newtype_index!` macro][rustc-nt] uses
//! [`global::NonZeroProgSymSize`] so that [`Option`] uses no
//! additional space (see [pull request `53315`][rustc-nt-pr]).
//! - Differences between TAMER and Rustc's implementations are outlined
//! above.
//!
//! [flyweight pattern]: https://en.wikipedia.org/wiki/Flyweight_pattern
//! [rust-string-cache]: https://github.com/servo/string-cache
//! [rust-string-interner]: https://github.com/robbepop/string-interner
//! [rfc-1845]: https://rust-lang.github.io/rfcs/1845-shared-from-slice.html
//! [rustc-intern]: https://doc.rust-lang.org/nightly/nightly-rustc/syntax/ast/struct.Name.html
//! [rustc-arena]: https://doc.rust-lang.org/nightly/nightly-rustc/arena/index.html
//! [rustc-nt]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_index/macro.newtype_index.html
//! [rustc-nt-pr]: https://github.com/rust-lang/rust/pull/53315
//!
//! The hash function chosen for this module is [Fx Hash][fxhash].
//!
//! - Rustc previously used the [Fowler-Noll-Vo (FNV)][fnv] hash
//! function,
//! but [now uses Fx Hash][rustc-fx].
//! This was extracted into the [`fxhash`][fxhash] crate,
//! which is used by TAMER.
//! - TAMER originally used FNV,
//! but benchmarks showed that Fx Hash was more performant.
//! - Benchmarks for other hash functions,
//! including FNV,
//! can be found at the [`hash-rs`][hash-rs] project.
//!
//! [fnv]: https://doc.servo.org/fnv/
//! [rustc-fx]: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_data_structures/fx/index.html
//! [hash-rs]: https://github.com/Gankra/hash-rs
use crate::global;
use bumpalo::Bump;
use fxhash::FxBuildHasher;
use std::cell::RefCell;
use std::collections::HashMap;
use std::convert::TryInto;
use std::fmt;
use std::hash::BuildHasher;
use std::ops::Deref;
/// Unique symbol identifier.
///
/// _Do not construct this value yourself;_
/// use an [`Interner`].
///
/// This newtype helps to prevent other indexes from being used where a
/// symbol index is expected.
/// Note, however, that it provides no defense against mixing symbol indexes
/// between multiple [`Interner`]s.
///
/// The index `0` is never valid because of [`global::NonZeroProgSymSize`],
/// which allows us to have `Option<SymbolIndex>` at no space cost.
#[derive(Copy, Clone, Debug, PartialEq, Eq)]
pub struct SymbolIndex(global::NonZeroProgSymSize);
impl SymbolIndex {
/// Construct index from a non-zero `u32` value.
///
/// Panics
/// ------
/// Will panic if `n == 0`.
pub fn from_u32(n: u32) -> SymbolIndex {
SymbolIndex(global::NonZeroProgSymSize::new(n).unwrap())
}
/// Construct index from an unchecked non-zero `u32` value.
///
/// This does not verify that `n > 0` and so must only be used in
/// contexts where this invariant is guaranteed to hold.
/// Unlike [`from_u32`](SymbolIndex::from_u32),
/// this never panics.
unsafe fn from_u32_unchecked(n: u32) -> SymbolIndex {
SymbolIndex(global::NonZeroProgSymSize::new_unchecked(n))
}
}
impl From<SymbolIndex> for usize {
fn from(value: SymbolIndex) -> usize {
value.0.get() as usize
}
}
impl<'i> From<&Symbol<'i>> for SymbolIndex {
fn from(sym: &Symbol<'i>) -> Self {
sym.index()
}
}
/// Interned string.
///
/// A reference to this symbol is returned each time the same string is
/// interned with the same [`Interner`];
/// as such,
/// symbols can be compared for equality by pointer;
/// the underlying symbol id need not be used.
///
/// Each symbol is identified by a unique integer
/// (see [`index`](Symbol::index)).
/// The use of integers creates a more dense range of values than pointers,
/// which allows callers to use a plain [`Vec`] as a map instead of
/// something far more expensive like
/// [`HashSet`](std::collections::HashSet);
/// this is especially beneficial for portions of the system that make
/// use of nearly all interned symbols,
/// like the ASG.
/// A [`SymbolIndex`] can be mapped back into its [`Symbol`] by calling
/// [`Interner::index_lookup`] on the same interner that produced it.
///
/// The symbol also stores a string slice referencing the interned string
/// itself,
/// whose lifetime is that of the [`Interner`]'s underlying data store.
/// Dereferencing the symbol will expose the underlying slice.
#[derive(Copy, Clone, Debug)]
pub struct Symbol<'i> {
index: SymbolIndex,
str: &'i str,
}
impl<'i> Symbol<'i> {
/// Construct a new interned value.
///
/// _This must only be done by an [`Interner`]._
/// As such,
/// this function is not public.
///
/// For test builds (when `cfg(test)`),
/// `new_dummy` is available to create symbols for tests.
#[inline]
fn new(index: SymbolIndex, str: &'i str) -> Symbol<'i> {
Self { index, str }
}
/// Retrieve unique symbol index.
///
/// This is a densely-packed identifier that can be used as an index for
/// mapping.
/// See [`SymbolIndex`] for more information.
#[inline]
pub fn index(&self) -> SymbolIndex {
self.index
}
/// Construct a new interned value _for testing_.
///
/// This is a public version of [`Symbol::new`] available for test
/// builds.
/// This separate name is meant to strongly imply that you should not be
/// doing this otherwise.
///
/// See also `dummy_symbol!`.
#[cfg(test)]
#[inline(always)]
pub fn new_dummy(index: SymbolIndex, str: &'i str) -> Symbol<'i> {
Self::new(index, str)
}
}
impl<'i> PartialEq for Symbol<'i> {
fn eq(&self, other: &Self) -> bool {
std::ptr::eq(self as *const _, other as *const _)
|| std::ptr::eq(self.str.as_ptr(), other.str.as_ptr())
}
}
impl<'i> Eq for Symbol<'i> {}
impl<'i> Deref for Symbol<'i> {
type Target = str;
/// Dereference to interned string slice.
///
/// This allows for symbols to be used where strings are expected.
#[inline]
fn deref(&self) -> &str {
self.str
}
}
impl<'i> fmt::Display for Symbol<'i> {
/// Display name of underlying string.
///
/// Since symbols contain pointers to their interned slices,
/// we effectively get this for free.
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.str)
}
}
/// Create, store, compare, and retrieve [`Symbol`] values.
///
/// Interners accept string slices and produce values of type [`Symbol`].
/// A reference to the same [`Symbol`] will always be returned for a given
/// string,
/// allowing symbols to be compared for equality cheaply by comparing
/// pointers.
/// Symbol locations in memory are fixed for the lifetime of the interner.
///
/// If you care whether a value has been interned yet or not,
/// see [`intern_soft`][Interner::intern_soft`] and
/// [`contains`](Interner::contains).
///
/// See the [module-level documentation](self) for an example.
pub trait Interner<'i> {
/// Intern a string slice or return an existing [`Symbol`].
///
/// If the provided string has already been interned,
/// then a reference to the existing [`Symbol`] will be returned.
/// Otherwise,
/// the string will be interned and a new [`Symbol`] created.
///
/// The lifetime of the returned symbol is bound to the lifetime of the
/// underlying intern pool.
///
/// To retrieve an existing symbol _without_ interning,
/// see [`intern_soft`](Interner::intern_soft).
fn intern(&'i self, value: &str) -> &'i Symbol<'i>;
/// Retrieve an existing intern for the string slice `s`.
///
/// Unlike [`intern`](Interner::intern),
/// this will _not_ intern the string if it has not already been
/// interned.
fn intern_soft(&'i self, value: &str) -> Option<&'i Symbol<'i>>;
/// Determine whether the given value has already been interned.
fn contains(&self, value: &str) -> bool;
/// Number of interned strings.
///
/// This count will increase each time a unique string is interned.
/// It does not increase when a string is already interned.
fn len(&self) -> usize;
/// Look up a previously interned [`Symbol`] by its [`SymbolIndex`].
///
/// This will always return a [`Symbol`] as long as the provided `index`
/// represents a symbol interned with this interner.
/// If the index is not found,
/// the result is [`None`].
///
/// This method is most useful when storing [`Symbol`] is not possible
/// or desirable.
/// For example,
/// borrowed [`Symbol`] references require lifetimes,
/// whereas [`SymbolIndex`] is both owned _and_ [`Copy`].
/// [`SymbolIndex`] is also much smaller than [`Symbol`].
fn index_lookup(&'i self, index: SymbolIndex) -> Option<&'i Symbol<'i>>;
/// Intern an assumed-UTF8 slice of bytes or return an existing
/// [`Symbol`].
///
/// Safety
/// ======
/// This function is unsafe because it uses
/// [`std::str::from_utf8_unchecked`].
/// It is provided for convenience when interning from trusted binary
/// data
/// (such as [object files][]).
///
/// [object files]: crate::obj
unsafe fn intern_utf8_unchecked(&'i self, value: &[u8]) -> &'i Symbol<'i> {
self.intern(std::str::from_utf8_unchecked(value))
}
}
/// An interner backed by an [arena](bumpalo).
///
/// Since interns exist until the interner itself is freed,
/// an arena is a much more efficient and appropriate memory allocation
/// strategy.
/// This further provides a stable location in memory for symbol data.
///
/// For the recommended configuration,
/// see [`DefaultInterner`].
///
/// See the [module-level documentation](self) for examples and more
/// information on how to use this interner.
pub struct ArenaInterner<'i, S>
where
S: BuildHasher + Default,
{
/// String and [`Symbol`] storage.
arena: Bump,
/// Symbol references by index.
///
/// This vector enables looking up a [`Symbol`] using its
/// [`SymbolIndex`].
///
/// The first index must always be populated during initialization to
/// ensure that [`SymbolIndex`] will never be `0`.
indexes: RefCell<Vec<&'i Symbol<'i>>>,
/// Map of interned strings to their respective [`Symbol`].
///
/// Both strings and symbols are allocated within `arena`.
map: RefCell<HashMap<&'i str, &'i Symbol<'i>, S>>,
}
lazy_static! {
/// Dummy [`Symbol`] for use at index `0`.
///
/// A symbol must never have an index of `0`,
/// so this can be used as a placeholder.
/// The chosen [`SymbolIndex`] here does not matter since this will
/// never be referenced.
static ref DUMMY_SYM: Symbol<'static> =
Symbol::new(SymbolIndex::from_u32(1), "!BADSYMREF!");
}
impl<'i, S> ArenaInterner<'i, S>
where
S: BuildHasher + Default,
{
/// Initialize a new interner with no initial capacity.
///
/// Prefer [`with_capacity`](ArenaInterner::with_capacity) when possible.
#[inline]
pub fn new() -> Self {
Self::with_capacity(0)
}
/// Initialize a new interner with an initial capacity for the
/// underlying [`HashMap`].
///
/// The given `capacity` has no affect on arena allocation.
/// Specifying initial capacity is important only for the map of strings
/// to symbols because it will reallocate and re-hash its contents
/// once capacity is exceeded.
/// See benchmarks.
///
/// If reallocation is a major concern,
/// a [consistent hashing algorithm][consistent] could be considered,
/// but the implementation will still incur the cost of copying
/// the [`HashMap`]'s contents to a new location in memory.
///
/// [consistent]: https://en.wikipedia.org/wiki/Consistent_hashing
#[inline]
pub fn with_capacity(capacity: usize) -> Self {
let mut indexes = Vec::<&'i Symbol<'i>>::with_capacity(capacity);
// The first index is not used since SymbolIndex cannot be 0.
indexes.push(&DUMMY_SYM);
Self {
arena: Bump::new(),
indexes: RefCell::new(indexes),
map: RefCell::new(HashMap::with_capacity_and_hasher(
capacity,
Default::default(),
)),
}
}
}
impl<'i, S> Interner<'i> for ArenaInterner<'i, S>
where
S: BuildHasher + Default,
{
fn intern(&'i self, value: &str) -> &'i Symbol<'i> {
let mut map = self.map.borrow_mut();
if let Some(sym) = map.get(value) {
return sym;
}
let mut syms = self.indexes.borrow_mut();
let next_index: u32 = syms
.len()
.try_into()
.expect("internal error: SymbolIndex range exhausted");
// This is not actually unsafe because next_index is always >0
// from initialization.
debug_assert!(next_index != 0);
let id = unsafe { SymbolIndex::from_u32_unchecked(next_index) };
// Copy string slice into the arena.
let clone: &'i str = unsafe {
&*(std::str::from_utf8_unchecked(
self.arena.alloc_slice_clone(value.as_bytes()),
) as *const str)
};
// Symbols are also stored within the arena, adjacent to the
// string. This ensures that both have stable locations in memory.
let sym: &'i Symbol<'i> = self.arena.alloc(Symbol::new(id, clone));
map.insert(clone, sym);
syms.push(sym);
sym
}
#[inline]
fn intern_soft(&'i self, value: &str) -> Option<&'i Symbol<'i>> {
self.map.borrow().get(value).map(|sym| *sym)
}
#[inline]
fn contains(&self, value: &str) -> bool {
self.map.borrow().contains_key(value)
}
#[inline]
fn len(&self) -> usize {
self.map.borrow().len()
}
fn index_lookup(&'i self, index: SymbolIndex) -> Option<&'i Symbol<'i>> {
self.indexes
.borrow()
.get(index.0.get() as usize)
.map(|sym| *sym)
}
}
/// Interner using the [Fx Hash][fxhash] hashing function.
///
/// _This is currently the hash function used by [`DefaultInterner`]._
///
/// If denial of service is not a concern,
/// then this will outperform the default
/// [`DefaultHasher`](std::collections::hash_map::DefaultHasher)
/// (which uses SipHash at the time of writing).
///
/// See intern benchmarks for a comparison.
pub type FxArenaInterner<'i> = ArenaInterner<'i, FxBuildHasher>;
/// Recommended [`Interner`] and configuration.
///
/// The choice of this default relies on the assumption that
/// denial-of-service attacks against the hash function are not a
/// concern.
///
/// For more information on the hashing algorithm,
/// see [`FxArenaInterner`].
pub type DefaultInterner<'i> = FxArenaInterner<'i>;
/// Concisely define dummy symbols for testing.
#[cfg(test)]
macro_rules! symbol_dummy {
($id:expr, $name:expr) => {
Symbol::new_dummy(SymbolIndex::from_u32($id), $name);
};
}
#[cfg(test)]
mod test {
use super::*;
mod symbol {
use super::*;
/// Option<Symbol> should have no space cost.
#[test]
fn symbol_index_option_no_cost() {
use std::mem::size_of;
assert_eq!(
size_of::<Option<Symbol>>(),
size_of::<Symbol>(),
"Option<Symbol> should be the same size as Symbol"
);
}
#[test]
fn self_compares_eq() {
let sym = Symbol::new(SymbolIndex::from_u32(1), "str");
assert_eq!(&sym, &sym);
}
#[test]
fn copy_compares_equal() {
let sym = Symbol::new(SymbolIndex::from_u32(1), "str");
let cpy = sym;
assert_eq!(sym, cpy);
}
// Integer values are for convenience, not identity. They cannot be
// used as a unique identifier across different interners.
#[test]
fn same_index_different_slices_compare_unequal() {
let a = Symbol::new(SymbolIndex::from_u32(1), "a");
let b = Symbol::new(SymbolIndex::from_u32(1), "b");
assert_ne!(a, b);
}
// As mentioned above, ids are _not_ the identity of the symbol. If
// two values point to the same location in memory, they are assumed
// to have come from the same interner, and should therefore have
// the same index this should never happen unless symbols are
// being created without the use of interners, which is unsupported.
//
// This test is a cautionary tale.
#[test]
fn different_index_same_slices_compare_equal() {
let slice = "str";
let a = Symbol::new(SymbolIndex::from_u32(1), slice);
let b = Symbol::new(SymbolIndex::from_u32(2), slice);
assert_eq!(a, b);
}
#[test]
fn cloned_symbols_compare_equal() {
let sym = Symbol::new(SymbolIndex::from_u32(1), "foo");
assert_eq!(sym, sym.clone());
}
// &Symbol can be used where string slices are expected (this won't
// compile otherwise).
#[test]
fn ref_can_be_used_as_string_slice() {
let slice = "str";
let sym_slice: &str = &Symbol::new(SymbolIndex::from_u32(1), slice);
assert_eq!(slice, sym_slice);
}
// For use when we can guarantee proper ids.
#[test]
fn can_create_index_unchecked() {
assert_eq!(SymbolIndex::from_u32(1), unsafe {
SymbolIndex::from_u32_unchecked(1)
});
}
#[test]
fn can_retrieve_symbol_index() {
let index = SymbolIndex::from_u32(1);
assert_eq!(index, Symbol::new(index, "").index());
}
#[test]
fn displays_as_interned_value() {
let sym = Symbol::new(SymbolIndex::from_u32(1), "foo");
assert_eq!(format!("{}", sym), sym.str);
}
}
mod interner {
use super::*;
type Sut<'i> = DefaultInterner<'i>;
#[test]
fn recognizes_equal_strings() {
let a = "foo";
let b = a.to_string();
let c = "bar";
let d = c.to_string();
let sut = Sut::new();
let (ia, ib, ic, id) =
(sut.intern(a), sut.intern(&b), sut.intern(c), sut.intern(&d));
assert_eq!(ia, ib);
assert_eq!(&ia, &ib);
assert_eq!(*ia, *ib);
assert_eq!(ic, id);
assert_eq!(&ic, &id);
assert_eq!(*ic, *id);
assert_ne!(ia, ic);
assert_ne!(&ia, &ic);
assert_ne!(*ia, *ic);
}
#[test]
fn symbol_id_increases_with_each_new_intern() {
let sut = Sut::new();
// Remember that identifiers begin at 1
assert_eq!(
SymbolIndex::from_u32(1),
sut.intern("foo").index(),
"First index should be 1"
);
assert_eq!(
SymbolIndex::from_u32(1),
sut.intern("foo").index(),
"Index should not increment for already-interned symbols"
);
assert_eq!(
SymbolIndex::from_u32(2),
sut.intern("bar").index(),
"Index should increment for new symbols"
);
}
#[test]
fn length_increases_with_each_new_intern() {
let sut = Sut::new();
assert_eq!(0, sut.len(), "invalid empty len");
sut.intern("foo");
assert_eq!(1, sut.len(), "increment len");
// duplicate
sut.intern("foo");
assert_eq!(1, sut.len(), "do not increment len on duplicates");
sut.intern("bar");
assert_eq!(2, sut.len(), "increment len (2)");
}
#[test]
fn can_check_wither_string_is_interned() {
let sut = Sut::new();
assert!(!sut.contains("foo"), "recognize missing value");
sut.intern("foo");
assert!(sut.contains("foo"), "recognize interned value");
}
#[test]
fn intern_soft() {
let sut = Sut::new();
assert_eq!(None, sut.intern_soft("foo"));
let foo = sut.intern("foo");
assert_eq!(Some(foo), sut.intern_soft("foo"));
}
#[test]
fn new_with_capacity() {
let n = 512;
let sut = Sut::with_capacity(n);
// note that this is not publicly available
assert!(sut.map.borrow().capacity() >= n);
}
#[test]
fn intern_utf8_unchecked() {
let sut = Sut::new();
let a = sut.intern("foo");
let b = unsafe { sut.intern_utf8_unchecked(b"foo") };
assert_eq!(a, b);
}
#[test]
fn lookup_symbol_by_index() {
let sut = Sut::new();
// Symbol does not yet exist.
assert!(sut.index_lookup(SymbolIndex::from_u32(1)).is_none());
let sym = sut.intern("foo");
assert_eq!(Some(sym), sut.index_lookup(sym.index()));
assert_eq!(Some(sym), sut.index_lookup(sym.into()));
}
}
}
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