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use std::borrow::Borrow;
use std::cmp::Ordering;
use std::fmt;
use std::hash::Hash;
use std::hash::Hasher;
use std::marker::PhantomData;
use std::ops::Deref;
use delegate::delegate;
use merc_collections::ProtectionIndex;
use merc_unsafety::StablePointer;
use crate::Markable;
use crate::storage::Marker;
use crate::storage::SharedSymbol;
use crate::storage::THREAD_TERM_POOL;
/// The public interface for a function symbol. Can be used to write generic
/// functions that accept both [Symbol] and [SymbolRef].
///
/// See [crate::Term] for more information on how to use this trait with two lifetimes.
pub trait Symb<'a, 'b> {
/// Obtain the symbol's name.
fn name(&'b self) -> &'a str;
/// Obtain the symbol's arity.
fn arity(&self) -> usize;
/// Create a copy of the symbol reference.
fn copy(&'b self) -> SymbolRef<'a>;
/// Returns a unique index for the symbol.
fn index(&self) -> usize;
/// TODO: How to actually hide this implementation?
fn shared(&self) -> &SymbolIndex;
}
/// An alias for the type that is used to reference into the symbol set.
pub type SymbolIndex = StablePointer<SharedSymbol>;
/// A reference to a function symbol in the symbol pool.
#[repr(transparent)]
#[derive(Hash, PartialEq, Eq, PartialOrd, Ord)]
pub struct SymbolRef<'a> {
shared: SymbolIndex,
marker: PhantomData<&'a ()>,
/// Check that the SymbolRef is the same size as a usize.
#[cfg(not(debug_assertions))]
const _: () = assert!(std::mem::size_of::<SymbolRef>() == std::mem::size_of::<usize>());
/// Check that the Option<SymbolRef> is the same size as a usize using niche value optimisation.
const _: () = assert!(std::mem::size_of::<Option<SymbolRef>>() == std::mem::size_of::<usize>());
/// A reference to a function symbol with a known lifetime.
impl<'a> SymbolRef<'a> {
/// Protects the symbol from garbage collection, yielding a `Symbol`.
pub fn protect(&self) -> Symbol {
THREAD_TERM_POOL.with_borrow(|tp| tp.protect_symbol(self))
/// Internal constructor to create a `SymbolRef` from a `SymbolIndex`.
/// # Safety
/// We must ensure that the lifetime `'a` is valid for the returned `SymbolRef`.
pub unsafe fn from_index(index: &SymbolIndex) -> SymbolRef<'a> {
SymbolRef {
shared: index.copy(),
marker: PhantomData,
impl SymbolRef<'_> {
/// Internal constructo to convert any `Symb` to a `SymbolRef`.
pub(crate) fn from_symbol<'a, 'b, S: Symb<'a, 'b>>(symbol: &'b S) -> Self {
shared: symbol.shared().copy(),
impl<'a> Symb<'a, '_> for SymbolRef<'a> {
fn name(&self) -> &'a str {
unsafe { std::mem::transmute(self.shared.name()) }
fn arity(&self) -> usize {
self.shared.arity()
fn copy(&self) -> SymbolRef<'a> {
unsafe { SymbolRef::from_index(self.shared()) }
fn index(&self) -> usize {
self.shared.index()
fn shared(&self) -> &SymbolIndex {
&self.shared
impl Markable for SymbolRef<'_> {
fn mark(&self, marker: &mut Marker) {
marker.mark_symbol(self);
fn contains_term(&self, _term: &crate::aterm::ATermRef<'_>) -> bool {
false
fn contains_symbol(&self, symbol: &SymbolRef<'_>) -> bool {
self == symbol
fn len(&self) -> usize {
1
impl fmt::Display for SymbolRef<'_> {
fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
write!(f, "{}", self.name())
impl fmt::Debug for SymbolRef<'_> {
/// A protected function symbol, with the same interface as [SymbolRef].
pub struct Symbol {
symbol: SymbolRef<'static>,
root: ProtectionIndex,
impl Symbol {
/// Create a new symbol with the given name and arity.
pub fn new<N>(name: N, arity: usize) -> Symbol
where
N: Into<String> + AsRef<str>,
{
THREAD_TERM_POOL.with_borrow(|tp| tp.create_symbol(name, arity))
/// Internal constructor to create a symbol from an index and a root.
pub(crate) unsafe fn from_index(index: &SymbolIndex, root: ProtectionIndex) -> Symbol {
Self {
symbol: unsafe { SymbolRef::from_index(index) },
root,
/// Returns the root index, i.e., the index in the protection set. See `SharedTermProtection`.
pub fn root(&self) -> ProtectionIndex {
self.root
pub fn copy(&self) -> SymbolRef<'_> {
self.symbol.copy()
impl<'a> Symb<'a, '_> for &'a Symbol {
delegate! {
to self.symbol {
fn name(&self) -> &'a str;
fn copy(&self) -> SymbolRef<'a>;
impl<'a, 'b> Symb<'a, 'b> for Symbol
'b: 'a,
impl Drop for Symbol {
fn drop(&mut self) {
THREAD_TERM_POOL.with_borrow(|tp| {
tp.drop_symbol(self);
})
impl From<&SymbolRef<'_>> for Symbol {
fn from(value: &SymbolRef) -> Self {
value.protect()
impl Clone for Symbol {
fn clone(&self) -> Self {
self.copy().protect()
impl Deref for Symbol {
type Target = SymbolRef<'static>;
fn deref(&self) -> &Self::Target {
&self.symbol
impl fmt::Display for Symbol {
impl fmt::Debug for Symbol {
impl Hash for Symbol {
fn hash<H: Hasher>(&self, state: &mut H) {
self.copy().hash(state)
impl PartialEq for Symbol {
fn eq(&self, other: &Self) -> bool {
self.copy().eq(&other.copy())
impl PartialEq<SymbolRef<'_>> for Symbol {
fn eq(&self, other: &SymbolRef<'_>) -> bool {
self.copy().eq(other)
impl PartialOrd for Symbol {
fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
Some(self.cmp(other))
impl Ord for Symbol {
fn cmp(&self, other: &Self) -> Ordering {
self.copy().cmp(&other.copy())
impl Borrow<SymbolRef<'static>> for Symbol {
fn borrow(&self) -> &SymbolRef<'static> {
impl Eq for Symbol {}