Rename EvalState to Caches.

src/eval/cache.rs

@@ -0,0 +1,69 @@
+//! System caches.
+
+use crate::func::CallableFunction;
+use crate::{Identifier, StaticVec};
+use std::collections::BTreeMap;
+#[cfg(feature = "no_std")]
+use std::prelude::v1::*;
+
+/// _(internals)_ An entry in a function resolution cache.
+/// Exported under the `internals` feature only.
+#[derive(Debug, Clone)]
+pub struct FnResolutionCacheEntry {
+    /// Function.
+    pub func: CallableFunction,
+    /// Optional source.
+    /// No source if the string is empty.
+    pub source: Identifier,
+}
+
+/// _(internals)_ A function resolution cache.
+/// Exported under the `internals` feature only.
+///
+/// [`FnResolutionCacheEntry`] is [`Box`]ed in order to pack as many entries inside a single B-Tree
+/// level as possible.
+pub type FnResolutionCache = BTreeMap<u64, Option<Box<FnResolutionCacheEntry>>>;
+
+/// _(internals)_ A type containing system-wide caches.
+/// Exported under the `internals` feature only.
+///
+/// The following caches are contained inside this type:
+/// * A stack of [function resolution caches][FnResolutionCache]
+#[derive(Debug, Clone)]
+pub struct Caches(StaticVec<FnResolutionCache>);
+
+impl Caches {
+    /// Create an empty [`Caches`].
+    #[inline(always)]
+    #[must_use]
+    pub const fn new() -> Self {
+        Self(StaticVec::new_const())
+    }
+    /// Get the number of function resolution cache(s) in the stack.
+    #[inline(always)]
+    #[must_use]
+    pub fn fn_resolution_caches_len(&self) -> usize {
+        self.0.len()
+    }
+    /// Get a mutable reference to the current function resolution cache.
+    #[inline]
+    #[must_use]
+    pub fn fn_resolution_cache_mut(&mut self) -> &mut FnResolutionCache {
+        if self.0.is_empty() {
+            // Push a new function resolution cache if the stack is empty
+            self.push_fn_resolution_cache();
+        }
+        self.0.last_mut().unwrap()
+    }
+    /// Push an empty function resolution cache onto the stack and make it current.
+    #[allow(dead_code)]
+    #[inline(always)]
+    pub fn push_fn_resolution_cache(&mut self) {
+        self.0.push(BTreeMap::new());
+    }
+    /// Rewind the function resolution caches stack to a particular size.
+    #[inline(always)]
+    pub fn rewind_fn_resolution_caches(&mut self, len: usize) {
+        self.0.truncate(len);
+    }
+}